Run pydevd tests on github actions

[fabioz]

Right now the pydevd tests (which are run independent on debugpy) run on travis.org, but the tests seem to take a long time to start now (it seems travis.org will be deprecated in favor of travis.com).

Given that, I think the best approach is actually migrating to Github actions (I'm creating the issue here to track that I plan to tackle this right away as this slows down creating pull requests for debugpy as I wait for pydevd tests to run before submitting it to debugpy).