Consider using `act` to run GitHub Actions locally

[cosinekitty]

I just learned about this project:

https://github.com/nektos/act

It allows running GitHub Actions locally. This could help make it easier for new contributors to test changes without the complications of setting up a local build process. It could also help me when I make changes to a workflow yml file, so I don't have to make a lot of push noise to test/debug.