text: Title: envbindir behavior changed in tox4
  Body: ``` ini
  [tox]
  skipsdist = true
  envlist = py{37,38}
  [testenv]
  deps = flake8
  commands =
      py37: {[testenv:py37-flake8]commands}
      py38: {[testenv:py38-flake8]commands}
  [testenv:py{37,38}-flake8]
  commands = {envbindir}/flake8 --version
  ```
  ``` console
  $ venv/bin/tox --version
  3.28.0 imported from /tmp/tmp.5W879ZcLx9/venv/lib/python3.8/site-packages/tox/__init__.py
  $ venv/bin/tox
  py37 installed: flake8==5.0.4,importlib-metadata==4.2.0,mccabe==0.7.0,pycodestyle==2.9.1,pyflakes==2.5.0,typing_extensions==4.4.0,zipp==3.12.0
  py37 run-test-pre: PYTHONHASHSEED='335891262'
  py37 run-test: commands[0] | /tmp/tmp.5W879ZcLx9/.tox/py37/bin/flake8 --version
  5.0.4 (mccabe: 0.7.0, pycodestyle: 2.9.1, pyflakes: 2.5.0) CPython 3.7.13 on
  Linux
  py38 installed: flake8==6.0.0,mccabe==0.7.0,pycodestyle==2.10.0,pyflakes==3.0.1
  py38 run-test-pre: PYTHONHASHSEED='335891262'
  py38 run-test: commands[0] | /tmp/tmp.5W879ZcLx9/.tox/py38/bin/flake8 --version
  6.0.0 (mccabe: 0.7.0, pycodestyle: 2.10.0, pyflakes: 3.0.1)
  CPython 3.8.10 on Linux
  ____________________________ summary _____________________________
    py37: commands succeeded
    py38: commands succeeded
    congratulations :)
  ```
  - Note how `{envbindir}` was substituted using the name of the env being _run_:
    > py38 run-test: commands[0] | /tmp/tmp.5W879ZcLx9/.tox/py38/bin/flake8 --version
  ``` console
  $ venv/bin/tox --version
  4.4.2 from /tmp/tmp.5W879ZcLx9/venv/lib/python3.8/site-packages/tox/__init__.py
  $ venv/bin/tox
  py37: commands[0]> .tox/py37-flake8/bin/flake8 --version
  py37: exit 2 (0.01 seconds) /tmp/tmp.5W879ZcLx9> .tox/py37-flake8/bin/flake8 --version
  py37: FAIL ✖ in 0.1 seconds
  py38: commands[0]> .tox/py38-flake8/bin/flake8 --version
  py38: exit 2 (0.00 seconds) /tmp/tmp.5W879ZcLx9> .tox/py38-flake8/bin/flake8 --version
    py37: FAIL code 2 (0.10=setup[0.09]+cmd[0.01] seconds)
    py38: FAIL code 2 (0.02=setup[0.02]+cmd[0.00] seconds)
    evaluation failed :( (0.23 seconds)
  ```
  - Note how the `{envbindir}` substitution changed to the name of the env being _referenced_:
    > py38: commands[0]> .tox/py38-flake8/bin/flake8 --version
  
  Was this intentional?