ci: refactor unit test CI workflow

[AngryMaciek]

I'd suggest to merge python-tests-mac.yml and python-tests.yml files into one.
GH Actions YAML syntax allow to execute CI workflows on multiple platforms (check here).
If you need to execute a command specifically to only one of the systems you can conditionalize on the runner specifications.

Edit:

If I see this correctly, currently both CI workflows run the unit testing framework<?>
So I would change the name of the (merged) GH shield to unit