Useless combo of `docker-image` and `target-python-version`

[klando]

Felix Fontein clarified a point about docker imageS and (target) python versionS in ansible-test: it's either one or the other, but using a named docker image + a specific python target is not of interest (the default docker image is the one to use for testing with several python target).

I didn't understood that before...

As a consequence it might be of interest to outline that in this Action, and eventually pretends to prevent bad combination of options, something this PR does not address at all.

[webknjaz]

Feel free to send a PR updating the README and maybe adding a warning annotation via runner commands. Here's an example: https://github.com/pypa/gh-action-pypi-publish/blob/bea5cda/twine-upload.sh#L10-L18.

[felixfontein]

Images can contain multiple Python version (for example the default image does), for such images the explicit Python version is useful. For other images it usually is not.

[webknjaz]

@felixfontein are you saying that a runtime warning would be disturbing the UX, and we just need to mention this in the docs?

[felixfontein]

It depends.

For sanity tests, you should always use the default container and never specify target-python-version.

For unit tests, you should always use the default container, but specifying target-python-version can make sense (if you want to split up unit tests per Python version - useful if running them for one Python version takes a long time).

For integration tests, all containers can make sense, and whether target-python-version makes sense depends on the container. It should always be specified for the default container, it should never be specified for most OS containers coming with ansible-test, and it must always be specified for custom containers.

[webknjaz]

Got it. Feel free to send a PR with your vision. I don't have strong opinions on this so won't prioritize implementing the solution.