Drop support for Ruby 3.0, and adopt Rubycritic changes for Ruby 3.1.

[faisal]

While we have not yet dropped support for Ruby 2.7 (EOL'd over a year ago), Ruby 3.0 EOL'd a couple months ago and this PR does the work to move forward from there.

• Drop support for Ruby 3.0.
• Update Rubycritic config to target Ruby 3.1. Apply all safe autocorrections except for Style/HashSyntax.
• Set Rubycritic's Style/HashSyntax EnforcedShorthandSyntax to 'never', which keeps the old style in place (and consistent) until we decide to convert.
• Add Ruby 3.3 to the test matrix and Drop Ruby 3.0.
• Bump minitest, mocha, rubocop dependencies

Check list:

• [X] Add an entry to the changelog
• [X] Squash all commits into a single one
• [X] Describe your PR, link issues, etc.