Add initial push GHA workflow

[eigenbeam]

No description provided.

[eigenbeam]

@juliacollins Here's a minimal GitHub actions workflow that will run pytest.

I skipped two tests that fail since they were written to require something on the filesystem, and it isn't there in the GitHub actions environment. My thought was that we need to fix those tests anyway so that they don't require directories & files (mock / stub the dirs/files), but I can do that work in my in-progress branch.

In other words, you could review this PR with those two tests skipped, knowing I'll fix them in another branch. Or if you prefer, I can fix them here in this PR. Either way is fine.

[eigenbeam]

@juliacollins I fixed the two unit tests that I had marked as skipped. So this should be ready to review.

[juliacollins]

Excellent, you have provided a couple of mock examples for me to follow!