Test attr_encrypted in Ruby 3

Related to #369392 (closed)

As noted, attr_encrypted is un-maintained. We have patched one place where kwarg fails with Ruby 3.

Proposal

1. Add tests in GitLab that we can encrypt, and decrypt database values correctly in Ruby 3
2. Or, fork attr_encrypted as attr_encrypted_gitlab, and run Ruby 3 tests on it

/cc @mkaeppler