Testing in GitHub CI

At the moment, it seems like only the docs are checked when submitting a PR - and only for Python 3.9. This does not seem to be sufficient, as test breakages are not visible automatically by this, for example because of another Python version in the supported range 3.7 to 3.12.

When already at it: It seems like this repository does not have any contribution docs like ScanCode Toolkit: https://github.com/nexB/scancode-toolkit/blob/develop/CONTRIBUTING.rst Do the same rules apply here?