requires in [tox] breaks factoring out environments

[bittner]

Describe the bug
When I add a requires to Tox' main section the plugin stops factoring out the Tox environments. Jobs on GHA will run all Tox environments instead of just a single one.

To Reproduce

Add, e.g., the following to your tox.ini:

[tox]
envlist = py3{5,6,7,8,9,10,11}
requires = virtualenv<20.22.0

[gh-actions]
python =
    2.7: py27
    3.5: py35
    3.6: py36
    3.7: py37
    3.8: py38
    3.9: py39
    3.10: py310
    3.11: py311

Irritatingly, this behavior is not consistent across all jobs spawned on GHA.

See bittner/pyclean#66 (Actions) for an example of failing test jobs.

Expected behavior
tox-gh-actions should produce separate jobs on GHA, running tests for only a single Tox environment (e.g. Python version).

[ymyzk]

Could you try adding tox-gh-actions to requires as well? See #102 (comment) for more context on this.

This is explained in README for tox-gh-actions v2, but not in one for v3. I'll also make sure to update the README.