GitHub Actions changes

[Kriti Godey]

I needed something quick and easy to work on, so I fixed a bunch of GitHub workflow issues here https://github.com/centerofci/mathesar/pull/2673. I'll merge and test them, but FYI any wonky GitHub actions stuff going on in the next few days.

I made a lot of the workflows conditional, so frontend tests only run on PRs that change frontend code, backend tests ignore frontend and docs changes, and docs PRs run CI. Please double check that PRs are running appropriate checks before you merge them,