text: Title: Can not set number of worker processes for run-parallel when no spinner is shown
  Body: ## Issue
  
  Can not set number of worker processes for tox `run-parallel` command via `--parallel` option or `TOX_PARALLEL` environment variable if spinner is disabled via `--parallel-no-spinner` option or `CI` environment variable. Numeric value of `--parallel` option gets ignored and maximum number of workers is always used (which is probably equal to number of CPU cores). The issue results in OOM (out-of-memory) on build agents using `run-parallel` with `CI` environment variable set.
  
  ## Environment
  
  Tox 4.11.4 works as expected. Newer versions exhibit the issue. Git blame points to https://github.com/tox-dev/tox/commit/7bbf89ef04fbb5651aa2e0c46dc020869842fc0e#diff-40a5f9d4fad958c6e6fb3bd9cf117200f0b4a8a23284e850b38a80477f3b2d9dR86
  
  ![Image](https://github.com/user-attachments/assets/fbe69662-ed92-48b7-8385-f5cbd6775093)
  
  ## Output of running tox
  
  Actual behaviour (run-parallel in 2 jobs):
  ```console
   $ tox run-parallel --parallel 2 --parallel-no-spinner -x 'tox.envlist=job-{a,b,c,d,e}'
  job-e: OK ✔ in 10.14 seconds
  job-b: OK ✔ in 10.15 seconds
  job-c: OK ✔ in 10.15 seconds
  job-d: OK ✔ in 10.15 seconds
    job-a: OK (10.15=setup[0.10]+cmd[10.03,0.02] seconds)
    job-b: OK (10.15=setup[0.10]+cmd[10.03,0.02] seconds)
    job-c: OK (10.15=setup[0.10]+cmd[10.04,0.02] seconds)
    job-d: OK (10.15=setup[0.10]+cmd[10.03,0.02] seconds)
    job-e: OK (10.14=setup[0.10]+cmd[10.02,0.02] seconds)
    congratulations :) (10.22 seconds)
  ```
  
  Expected behavoiur:
  
  ```console
  $ tox run-parallel --parallel 2 --parallel-no-spinner -x 'tox.envlist=job-{a,b,c,d,e}'
  job-b: OK ✔ in 10.09 seconds
  job-a: OK ✔ in 10.1 seconds
  job-c: OK ✔ in 10.06 seconds
  job-d: OK ✔ in 10.06 seconds
    job-a: OK (10.10=setup[0.06]+cmd[10.03,0.02] seconds)
    job-b: OK (10.09=setup[0.06]+cmd[10.02,0.02] seconds)
    job-c: OK (10.06=setup[0.02]+cmd[10.03,0.02] seconds)
    job-d: OK (10.06=setup[0.02]+cmd[10.03,0.02] seconds)
    job-e: OK (10.06=setup[0.01]+cmd[10.03,0.02] seconds)
    congratulations :) (30.28 seconds)
  ```
  
  i.e. execution should took around 30 seconds, not 10.
  ## Minimal example
  
  ```console
  [tox]
  
  [testenv]
  commands =
      job: python -c 'import time;time.sleep(10)'
      a,b,c,d,e: python -c 'print("ok")'
  ```