Add Ruby 3.0 and 3.1 to CI

[petergoldstein]

This PR adds Ruby 3.0 and 3.1 to CI and updates the CI Ruby/Rails matrix accordingly. Changes outside of the workflow definition include:

• Adding an explicit gem webrick line to the Gemfile(s) when the Ruby version is 3.0 or greater
• Adding explicit lines for net-smtp, net-imap, and net-pop when the Ruby version is 3.1 or greater to both relevant Gemfiles and the IDP template file.

This PR doesn't include Rails 7, as getting that working properly requires a bit more work with views and UI behavior.

[petergoldstein]

Great, thanks. I'm working on getting Rails 7 in now. It's a little involved because the ruby-saml-idp gem is unmaintained and is incompatible with zeitwerk class loading. I'm finishing up an updated, maintained version of that gem that can be used by devise_saml_authenticatable going forward.

[petergoldstein]

@adamstegman On a related note, is there a reason the support matrix is so wide? It goes back to Rails 4.0 and Ruby 2.0.

Ruby 2.5 was EOLed earlier this year. Limiting it to Ruby 2.5+ or Ruby 2.6+ would simplify things.

Similarly, Rails 5.1 was EOLed over 2 years ago. Limiting it to Rails 5.2+ would also simplify things.

[adamstegman]

Good point! We can probably drop support for versions that are no longer supported upstream without having to bump a major version.

Thanks for digging into Rails 7 too!

[petergoldstein]

@adamstegman If you're good with those changes I'll put up a PR to trim CI to Ruby 2.6+ and Rails 5.2+