Add support for ruby 3

[federicoaldunate]

Summary

Add support for ruby 3

Also, exclude rails 5.2 and ruby 3 from the test matrix. https://github.com/rails/rails/issues/40938

We need to figure out if a test is valid for ruby 3

Other Information

• [ ] Pagy's upgrade is merged https://github.com/rootstrap/exception_hunter/pull/127

[brunvez]

Niiice, can you resolve the conflict @federicoaldunate? If not I'll do it