Add Github Actions tests to detect breakages

[tannisroot]

The project seems to suffer a lot from changes pushed to main branch that completely break basic functionality.
I think adding basic tests that run through Github Actions might be worthwhile.

[florian-asche]

I can add workflows but i need help with the tests, test tool for python...

[jaminh]

The scripts for running format checks, linting, and unit tests (pytest) already exist in the scripts directory. Your github actions should be able to just execute those scripts. There aren't currently any actual tests defined to run, but it would still be worthwhile to run the linter and have it set up for the unit tests, and we can add actual tests later.

I'll also submit a PR to move some of the MPV smoke tests out of the tests directory because they aren't actually proper pytest unit tests, and it always startles me when my speakers start playing French music I'm not expecting.