Migrate CI to GitHub Actions with Ruby 3.2

[petergoldstein]

This PR migrates CI to GitHub Actions as Travis CI.org is no longer active.

Given that the Gemfile runs with Rails 7, we're running those Rubies which are compatible with Rails 7 (2.7, 3.0, 3.1, ruby-head).

To get the tests green on ruby-head, I fixed a minor issue in the param_set implementation where the Regexp operator =~ was being run against integers. Restricting such comparisons to strings resolves the issue.

Everything runs green on my fork.