Fix rspec tests and add testing for higher versions of Ruby/Rails

[emmahsax]

The tests on this repository needed a lot of work. They were only testing very outdated versions of Ruby and Rails, and the CI in GitHub Actions wasn't passing at all.

I learned most of this had to do with the specific versions of gems that were being installed for the given version of Ruby/Rails. Once I got to work ensuring the proper versions of gems were installed for each version of Ruby/Rails, then I started to get more consistent passing of the tests.

Then, I broadened the tests, and ensured they would pass for newer versions of Ruby/Rails, all the way up through Ruby 3.4 and Rails 8.0. I also pushed the tests down, so they're covering beginning with Rails 4.0 and Ruby 2.1.

At the end, I managed to get all tests passing with NO changes to the actual app, config, or lib directories, and MINIMAL changes to the spec directory.

The changes here could potentially affect when people try to run bundle install locally, as local development now defaults to Ruby 3.3.7 and Rails 7.2.2.1, and may decide to install different versions of gems such as concurrent-ruby, sprockets, and sqlite3.