Run tests via GitHub actions

[jdblischak]

This GitHub Actions pipeline will help find potential problems quickly. It installs the conda env and runs the tests scripts. It will run:

• whenever a code or data file is modified and pushed to the repo (or in a PR)
• automatically scheduled to run every 3 months
• it can also be triggered manually

You can see the passing jobs on my fork: https://github.com/jdblischak/polyfun/actions/workflows/ci.yml

I put the FINEMAP stuff in a separate commit in case you don't want to include it

[omerwe]

This is very cool, thanks so much @jdblischak!