Add Ruby 3.1 and Rails 7 to the CI matrix

[petergoldstein]

Adds Ruby 3.1 and Rails 7 to the CI matrix. To do this, the following additional changes were required:

1. Relaxing the allowed version of ruby/setup-ruby
2. Quoting the use of 3.0, to ensure that it is not truncated to 3.1

This runs green on my fork.

[petergoldstein]

This adds Ruby 3.2, fixes the GitHub Action config so we don't run into bundler issues related to Ruby 2.5/bundler 2.4 incompatibility, and fixes a few lints.