Run tests on Ruby 3 and remove LC_MESSAGES

[ofedoren]

Not so important, but still useful.

[chris1984]

Hey @ofedoren The tests are failing with ruby WARNING: File locale/bn/LC_MESSAGES/hammer-cli-katello.mo does not exist, generate with 'make all-mo'! No such file or directory @ rb_file_s_mtime - locale/bn/LC_MESSAGES/hammer-cli-katello.mo not found wrong number of arguments (given 2, expected 1)

Are you able to fix that up and we can merge this, I will make sure this gets in before branching.

[ofedoren]

@chris1984, the fix for that issue is to update rubocop, since it's quite outdated. I've tried to fix all of the offences and I did, but really really lazily, so please re-check after me :)

The only concern of mine is the changes in lib/hammer_cli_katello/content_import.rb. Please, could you ensure I didn't break the functionality (it's not covered by tests)? Essentially, you'd need to re-test #867 PR. These changes are because of https://www.rubydoc.info/gems/rubocop/RuboCop/Cop/Security/Open.

UPD: but hey, we're 🍏 on Ruby 3+ here :)