Fix CI and port to GitHub actions

[schneems]

I am standardizing on GitHub actions for zomboxom for CI as Circle has proven cumbersome. I've ported all the projects except those that use different versions of Rails. Such as:

• https://github.com/zombocom/wicked
• https://github.com/zombocom/maildown

Eventually, we need also to add tests for Rails 7 as well.

Help wanted

Also, I'm looking for help maintaining this project in the future. I ask anyone interested to please send a PR and mention that you're interested in helping. You can email me if you've previously had a commit merged in this project.

A maintainer will gain commit access and deploy access on rubygems if they don't have it already. A maintainer will be expected to:

• Update CI to keep tests passing and test new Ruby releases
• Review, merge, or close PRs
• Read and respond to issues
• Any feature or bugfix work that you desire

[schneems]

Example CI yml: https://github.com/zombocom/maildown/blob/main/.github/workflows/ci.yml