text: Title: set_env substitution doesn't pass PYTHONHASHSEED in tox 4.x
  Body: ## Issue
  
  Hi, I have encountered what I believe is tox bug.
  
  With 2 test environments: base (`[testenv]`) and non-base (`[testenv:hs]`), _some_ environment variables from the base one aren't set in the non-base when they are passed as a substitution, like:
  
  ```ini
  [testenv]
  setenv =
      PYTHONHASHSEED=0
      OTHER=foo
  
  [testenv:hs]
  setenv = {[testenv]setenv}
  ```
  
  In above example `PYTHONHASHSEED` will be random for every run of `tox -e has` and `OTHER` will be correctly set to foo. I found out that tox displays the same behaviour for some other variables, like `PATH`, but I didn't dig any further.
  
  Funny thing is that if we mix `setenv` and `set_env` a little bit, tox suddenly starts passing `PYTHONHASHSEED`, for example below tox.ini sets `PYTHONHASHSEED` to 0.
  
  ```ini
  [testenv]
  set_env =
      PYTHONHASHSEED=0
      OTHER=foo
  
  [testenv:hs]
  setenv = {[testenv]set_env}
  ```
  
  I checked this on tox 4.3.1, 4.3, 4.2, 4.1 and 4.0. Tox 3.x doesn't have this behaviour.
  
  Full tox.ini files attached below.
  
  ## Environment
  
  ## Output of running tox 
  
  Provide the output of `tox -rvv`:
  
  ```console
  using tox.ini: /home/mgoral/test/tox.ini (pid 279807)
    removing /home/mgoral/test/.tox/log
  could not satisfy requires MissingDependency(<Requirement('tox>=4.0')>)
  using tox-3.21.4 from /usr/lib/python3/dist-packages/tox/__init__.py (pid 279807)
  /usr/bin/python3 (/usr/bin/python3) is {'executable': '/usr/bin/python3', 'implementation': 'CPython', 'version_info': [3, 9, 2, 'final', 0], 'version': '3.9.2 (default, Feb 28 2021, 17:03:44) \n[GCC 10.2.1 20210110]', 'is_64': True, 'sysplatform': 'linux', 'extra_version_info': None}
  .tox uses /usr/bin/python3
  .tox start: getenv /home/mgoral/test/.tox/.tox
  .tox cannot reuse: -r flag
  .tox recreate: /home/mgoral/test/.tox/.tox
    removing /home/mgoral/test/.tox/.tox
  setting PATH=/home/mgoral/test/.tox/.tox/bin:/home/mgoral/.cargo/bin:/home/mgoral/.local/bin:/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games
  [279827] /home/mgoral/test/.tox$ /usr/bin/python3 -m virtualenv --no-download --python /usr/bin/python3 .tox
  created virtual environment CPython3.9.2.final.0-64 in 81ms
    creator CPython3Posix(dest=/home/mgoral/test/.tox/.tox, clear=False, no_vcs_ignore=False, global=False)
    seeder FromAppData(download=False, pip=bundle, setuptools=bundle, wheel=bundle, via=copy, app_data_dir=/home/mgoral/.local/share/virtualenv)
      added seed packages: pip==20.3.4, pkg_resources==0.0.0, setuptools==44.1.1, wheel==0.34.2
    activators BashActivator,CShellActivator,FishActivator,PowerShellActivator,PythonActivator,XonshActivator
  .tox installdeps: tox>=4.0
  setting PATH=/home/mgoral/test/.tox/.tox/bin:/home/mgoral/.cargo/bin:/home/mgoral/.local/bin:/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games
  [279835] /home/mgoral/test$ /home/mgoral/test/.tox/.tox/bin/python -m pip install 'tox>=4.0'
  Collecting tox>=4.0
    Using cached tox-4.3.1-py3-none-any.whl (147 kB)
  Collecting platformdirs>=2.6.2
    Using cached platformdirs-2.6.2-py3-none-any.whl (14 kB)
  Collecting virtualenv>=20.17.1
    Using cached virtualenv-20.17.1-py3-none-any.whl (8.8 MB)
  Collecting pyproject-api>=1.4
    Using cached pyproject_api-1.4.0-py3-none-any.whl (12 kB)
  Collecting pluggy>=1
    Using cached pluggy-1.0.0-py2.py3-none-any.whl (13 kB)
  Collecting chardet>=5.1
    Using cached chardet-5.1.0-py3-none-any.whl (199 kB)
  Collecting tomli>=2.0.1
    Using cached tomli-2.0.1-py3-none-any.whl (12 kB)
  Collecting filelock>=3.9
    Using cached filelock-3.9.0-py3-none-any.whl (9.7 kB)
  Collecting colorama>=0.4.6
    Using cached colorama-0.4.6-py2.py3-none-any.whl (25 kB)
  Collecting packaging>=23
    Using cached packaging-23.0-py3-none-any.whl (42 kB)
  Collecting cachetools>=5.2.1
    Using cached cachetools-5.2.1-py3-none-any.whl (9.3 kB)
  Collecting distlib<1,>=0.3.6
    Using cached distlib-0.3.6-py2.py3-none-any.whl (468 kB)
  Installing collected packages: tomli, platformdirs, packaging, filelock, distlib, virtualenv, pyproject-api, pluggy, colorama, chardet, cachetools, tox
  Successfully installed cachetools-5.2.1 chardet-5.1.0 colorama-0.4.6 distlib-0.3.6 filelock-3.9.0 packaging-23.0 platformdirs-2.6.2 pluggy-1.0.0 pyproject-api-1.4.0 tomli-2.0.1 tox-4.3.1 virtualenv-20.17.1
  .tox finish: getenv /home/mgoral/test/.tox/.tox after 3.43 seconds
  .tox start: finishvenv 
  write config to /home/mgoral/test/.tox/.tox/.tox-config1 as '409276cb52787e20907912730020ca0f84204a375c30a79fcb494ffde0e0f116 /usr/bin/python3\n3.21.4 0 0 0\n00000000000000000000000000000000 tox>=4.0'
  .tox finish: finishvenv  after 0.02 seconds
  .tox start: provision 
  [279851] /home/mgoral/test$ /home/mgoral/test/.tox/.tox/bin/python -m tox -rvv -e hs
  hs: 135 W remove tox env folder /home/mgoral/test/.tox/hs [tox/tox_env/api.py:321]
  hs: 159 I find interpreter for spec PythonSpec(major=3) [virtualenv/discovery/builtin.py:56]
  hs: 159 D discover exe for PythonInfo(spec=CPython3.9.2.final.0-64, exe=/home/mgoral/test/.tox/.tox/bin/python, platform=linux, version='3.9.2 (default, Feb 28 2021, 17:03:44) \n[GCC 10.2.1 20210110]', encoding_fs_io=utf-8-utf-8) in /usr [virtualenv/discovery/py_info.py:437]
  hs: 159 D filesystem is case-sensitive [virtualenv/info.py:24]
  hs: 160 D got python info of /usr/bin/python3.9 from /home/mgoral/.local/share/virtualenv/py_info/1/36cf16204b8548560b1c020c4e8fb5b57f0e4c58016f52f2d4be01e192833930.json [virtualenv/app_data/via_disk_folder.py:129]
  hs: 161 I proposed PythonInfo(spec=CPython3.9.2.final.0-64, system=/usr/bin/python3.9, exe=/home/mgoral/test/.tox/.tox/bin/python, platform=linux, version='3.9.2 (default, Feb 28 2021, 17:03:44) \n[GCC 10.2.1 20210110]', encoding_fs_io=utf-8-utf-8) [virtualenv/discovery/builtin.py:63]
  hs: 161 D accepted PythonInfo(spec=CPython3.9.2.final.0-64, system=/usr/bin/python3.9, exe=/home/mgoral/test/.tox/.tox/bin/python, platform=linux, version='3.9.2 (default, Feb 28 2021, 17:03:44) \n[GCC 10.2.1 20210110]', encoding_fs_io=utf-8-utf-8) [virtualenv/discovery/builtin.py:65]
  hs: 186 I create virtual environment via CPython3Posix(dest=/home/mgoral/test/.tox/hs, clear=False, no_vcs_ignore=False, global=False) [virtualenv/run/session.py:48]
  hs: 186 D create folder /home/mgoral/test/.tox/hs/bin [virtualenv/util/path/_sync.py:9]
  hs: 186 D create folder /home/mgoral/test/.tox/hs/lib/python3.9/site-packages [virtualenv/util/path/_sync.py:9]
  hs: 187 D write /home/mgoral/test/.tox/hs/pyvenv.cfg [virtualenv/create/pyenv_cfg.py:30]
  hs: 187 D 	home = /usr/bin [virtualenv/create/pyenv_cfg.py:34]
  hs: 187 D 	implementation = CPython [virtualenv/create/pyenv_cfg.py:34]
  hs: 187 D 	version_info = 3.9.2.final.0 [virtualenv/create/pyenv_cfg.py:34]
  hs: 187 D 	virtualenv = 20.17.1 [virtualenv/create/pyenv_cfg.py:34]
  hs: 187 D 	include-system-site-packages = false [virtualenv/create/pyenv_cfg.py:34]
  hs: 187 D 	base-prefix = /usr [virtualenv/create/pyenv_cfg.py:34]
  hs: 187 D 	base-exec-prefix = /usr [virtualenv/create/pyenv_cfg.py:34]
  hs: 187 D 	base-executable = /usr/bin/python3.9 [virtualenv/create/pyenv_cfg.py:34]
  hs: 187 D symlink /usr/bin/python3.9 to /home/mgoral/test/.tox/hs/bin/python [virtualenv/util/path/_sync.py:28]
  hs: 187 D create virtualenv import hook file /home/mgoral/test/.tox/hs/lib/python3.9/site-packages/_virtualenv.pth [virtualenv/create/via_global_ref/api.py:89]
  hs: 187 D create /home/mgoral/test/.tox/hs/lib/python3.9/site-packages/_virtualenv.py [virtualenv/create/via_global_ref/api.py:92]
  hs: 188 D ============================== target debug ============================== [virtualenv/run/session.py:50]
  hs: 188 D debug via /home/mgoral/test/.tox/hs/bin/python /home/mgoral/test/.tox/.tox/lib/python3.9/site-packages/virtualenv/create/debug.py [virtualenv/create/creator.py:197]
  hs: 188 D {
    "sys": {
      "executable": "/home/mgoral/test/.tox/hs/bin/python",
      "_base_executable": "/home/mgoral/test/.tox/hs/bin/python",
      "prefix": "/home/mgoral/test/.tox/hs",
      "base_prefix": "/usr",
      "real_prefix": null,
      "exec_prefix": "/home/mgoral/test/.tox/hs",
      "base_exec_prefix": "/usr",
      "path": [
        "/usr/lib/python39.zip",
        "/usr/lib/python3.9",
        "/usr/lib/python3.9/lib-dynload",
        "/home/mgoral/test/.tox/hs/lib/python3.9/site-packages"
      ],
      "meta_path": [
        "<class '_virtualenv._Finder'>",
        "<class '_frozen_importlib.BuiltinImporter'>",
        "<class '_frozen_importlib.FrozenImporter'>",
        "<class '_frozen_importlib_external.PathFinder'>"
      ],
      "fs_encoding": "utf-8",
      "io_encoding": "utf-8"
    },
    "version": "3.9.2 (default, Feb 28 2021, 17:03:44) \n[GCC 10.2.1 20210110]",
    "makefile_filename": "/usr/lib/python3.9/config-3.9-x86_64-linux-gnu/Makefile",
    "os": "<module 'os' from '/usr/lib/python3.9/os.py'>",
    "site": "<module 'site' from '/usr/lib/python3.9/site.py'>",
    "datetime": "<module 'datetime' from '/usr/lib/python3.9/datetime.py'>",
    "math": "<module 'math' (built-in)>",
    "json": "<module 'json' from '/usr/lib/python3.9/json/__init__.py'>"
  } [virtualenv/run/session.py:51]
  hs: 213 I add seed packages via FromAppData(download=False, pip=bundle, setuptools=bundle, wheel=bundle, via=copy, app_data_dir=/home/mgoral/.local/share/virtualenv) [virtualenv/run/session.py:55]
  hs: 215 D got embed update of distribution wheel from /home/mgoral/.local/share/virtualenv/wheel/3.9/embed/3/wheel.json [virtualenv/app_data/via_disk_folder.py:129]
  hs: 216 D got embed update of distribution setuptools from /home/mgoral/.local/share/virtualenv/wheel/3.9/embed/3/setuptools.json [virtualenv/app_data/via_disk_folder.py:129]
  hs: 216 D got embed update of distribution pip from /home/mgoral/.local/share/virtualenv/wheel/3.9/embed/3/pip.json [virtualenv/app_data/via_disk_folder.py:129]
  hs: 219 D install wheel from wheel /home/mgoral/test/.tox/.tox/lib/python3.9/site-packages/virtualenv/seed/wheels/embed/wheel-0.38.4-py3-none-any.whl via CopyPipInstall [virtualenv/seed/embed/via_app_data/via_app_data.py:47]
  hs: 219 D install setuptools from wheel /home/mgoral/test/.tox/.tox/lib/python3.9/site-packages/virtualenv/seed/wheels/embed/setuptools-65.6.3-py3-none-any.whl via CopyPipInstall [virtualenv/seed/embed/via_app_data/via_app_data.py:47]
  hs: 219 D install pip from wheel /home/mgoral/test/.tox/.tox/lib/python3.9/site-packages/virtualenv/seed/wheels/embed/pip-22.3.1-py3-none-any.whl via CopyPipInstall [virtualenv/seed/embed/via_app_data/via_app_data.py:47]
  hs: 220 D copy directory /home/mgoral/.local/share/virtualenv/wheel/3.9/image/1/CopyPipInstall/pip-22.3.1-py3-none-any/pip-22.3.1.dist-info to /home/mgoral/test/.tox/hs/lib/python3.9/site-packages/pip-22.3.1.dist-info [virtualenv/util/path/_sync.py:36]
  hs: 220 D copy /home/mgoral/.local/share/virtualenv/wheel/3.9/image/1/CopyPipInstall/setuptools-65.6.3-py3-none-any/setuptools-65.6.3.virtualenv to /home/mgoral/test/.tox/hs/lib/python3.9/site-packages/setuptools-65.6.3.virtualenv [virtualenv/util/path/_sync.py:36]
  hs: 220 D copy directory /home/mgoral/.local/share/virtualenv/wheel/3.9/image/1/CopyPipInstall/wheel-0.38.4-py3-none-any/wheel to /home/mgoral/test/.tox/hs/lib/python3.9/site-packages/wheel [virtualenv/util/path/_sync.py:36]
  hs: 221 D copy directory /home/mgoral/.local/share/virtualenv/wheel/3.9/image/1/CopyPipInstall/setuptools-65.6.3-py3-none-any/setuptools to /home/mgoral/test/.tox/hs/lib/python3.9/site-packages/setuptools [virtualenv/util/path/_sync.py:36]
  hs: 224 D copy directory /home/mgoral/.local/share/virtualenv/wheel/3.9/image/1/CopyPipInstall/pip-22.3.1-py3-none-any/pip to /home/mgoral/test/.tox/hs/lib/python3.9/site-packages/pip [virtualenv/util/path/_sync.py:36]
  hs: 227 D copy directory /home/mgoral/.local/share/virtualenv/wheel/3.9/image/1/CopyPipInstall/wheel-0.38.4-py3-none-any/wheel-0.38.4.dist-info to /home/mgoral/test/.tox/hs/lib/python3.9/site-packages/wheel-0.38.4.dist-info [virtualenv/util/path/_sync.py:36]
  hs: 229 D copy /home/mgoral/.local/share/virtualenv/wheel/3.9/image/1/CopyPipInstall/wheel-0.38.4-py3-none-any/wheel-0.38.4.virtualenv to /home/mgoral/test/.tox/hs/lib/python3.9/site-packages/wheel-0.38.4.virtualenv [virtualenv/util/path/_sync.py:36]
  hs: 231 D generated console scripts wheel-3.9 wheel3 wheel3.9 wheel [virtualenv/seed/embed/via_app_data/pip_install/base.py:41]
  hs: 256 D copy /home/mgoral/.local/share/virtualenv/wheel/3.9/image/1/CopyPipInstall/setuptools-65.6.3-py3-none-any/distutils-precedence.pth to /home/mgoral/test/.tox/hs/lib/python3.9/site-packages/distutils-precedence.pth [virtualenv/util/path/_sync.py:36]
  hs: 256 D copy directory /home/mgoral/.local/share/virtualenv/wheel/3.9/image/1/CopyPipInstall/setuptools-65.6.3-py3-none-any/pkg_resources to /home/mgoral/test/.tox/hs/lib/python3.9/site-packages/pkg_resources [virtualenv/util/path/_sync.py:36]
  hs: 264 D copy directory /home/mgoral/.local/share/virtualenv/wheel/3.9/image/1/CopyPipInstall/setuptools-65.6.3-py3-none-any/_distutils_hack to /home/mgoral/test/.tox/hs/lib/python3.9/site-packages/_distutils_hack [virtualenv/util/path/_sync.py:36]
  hs: 264 D copy directory /home/mgoral/.local/share/virtualenv/wheel/3.9/image/1/CopyPipInstall/setuptools-65.6.3-py3-none-any/setuptools-65.6.3.dist-info to /home/mgoral/test/.tox/hs/lib/python3.9/site-packages/setuptools-65.6.3.dist-info [virtualenv/util/path/_sync.py:36]
  hs: 265 D generated console scripts  [virtualenv/seed/embed/via_app_data/pip_install/base.py:41]
  hs: 286 D copy /home/mgoral/.local/share/virtualenv/wheel/3.9/image/1/CopyPipInstall/pip-22.3.1-py3-none-any/pip-22.3.1.virtualenv to /home/mgoral/test/.tox/hs/lib/python3.9/site-packages/pip-22.3.1.virtualenv [virtualenv/util/path/_sync.py:36]
  hs: 287 D generated console scripts pip3.9 pip3 pip-3.9 pip [virtualenv/seed/embed/via_app_data/pip_install/base.py:41]
  hs: 287 I add activators for Bash, CShell, Fish, Nushell, PowerShell, Python [virtualenv/run/session.py:61]
  hs: 288 D write /home/mgoral/test/.tox/hs/pyvenv.cfg [virtualenv/create/pyenv_cfg.py:30]
  hs: 288 D 	home = /usr/bin [virtualenv/create/pyenv_cfg.py:34]
  hs: 288 D 	implementation = CPython [virtualenv/create/pyenv_cfg.py:34]
  hs: 288 D 	version_info = 3.9.2.final.0 [virtualenv/create/pyenv_cfg.py:34]
  hs: 288 D 	virtualenv = 20.17.1 [virtualenv/create/pyenv_cfg.py:34]
  hs: 288 D 	include-system-site-packages = false [virtualenv/create/pyenv_cfg.py:34]
  hs: 288 D 	base-prefix = /usr [virtualenv/create/pyenv_cfg.py:34]
  hs: 288 D 	base-exec-prefix = /usr [virtualenv/create/pyenv_cfg.py:34]
  hs: 288 D 	base-executable = /usr/bin/python3.9 [virtualenv/create/pyenv_cfg.py:34]
  hs: 291 W commands[0]> python -c 'import os; print(os.environ["PYTHONHASHSEED"])' [tox/tox_env/api.py:427]
  288846098
  hs: 311 I exit 0 (0.02 seconds) /home/mgoral/test> python -c 'import os; print(os.environ["PYTHONHASHSEED"])' pid=279864 [tox/execute/api.py:275]
  hs: 312 W commands[1]> python -c 'import os; print(os.environ["OTHER"])' [tox/tox_env/api.py:427]
  foo
  hs: 327 I exit 0 (0.01 seconds) /home/mgoral/test> python -c 'import os; print(os.environ["OTHER"])' pid=279870 [tox/execute/api.py:275]
    hs: OK (0.19=setup[0.16]+cmd[0.02,0.01] seconds)
    congratulations :) (0.24 seconds)
  .tox finish: provision  after 0.39 seconds
  ```
  
  ## Minimal example
  
  tox.ini which doesn't pass `PYTHONHASHSEED` to `hs` environment, but passes `OTHER`:
  
  ```ini
  [tox]
  requires = tox>=4.0
  skipsdist = True
  
  [testenv]
  basepython = python3
  
  setenv =
      PYTHONHASHSEED=0
      OTHER=foo
  
  [testenv:hs]
  commands =
      python -c 'import os; print(os.environ["PYTHONHASHSEED"])'
      python -c 'import os; print(os.environ["OTHER"])'
  
  setenv = {[testenv]setenv}
  ```
  
  tox.ini which passes `PYTHONHASHSEED` to `hs` environment (watch the underscores in set_env and setenv)
  
  ```ini
  [tox]
  requires = tox>=4.0
  skipsdist = True
  
  [testenv]
  basepython = python3
  
  set_env =
      PYTHONHASHSEED=0
      OTHER=foo
  
  [testenv:hs]
  commands =
      python -c 'import os; print(os.environ["PYTHONHASHSEED"])'
      python -c 'import os; print(os.environ["OTHER"])'
  
  setenv = {[testenv]set_env}
  
  ```
  