Update to Ruby 3

[peerkleio]

Updates the gem to use Ruby v3. This also updates the CI runs to use multiple versions of Ruby and ActiveRecord while excluding incompatible versions (e.g. Ruby 3.2 won't work with Rails 6.1)

Other code changes that were necessary,

1. Replace update_attributes with update_attribute as the former has been deprecated.
2. Update a call to ActiveRecord::MigrationContext with additional argument required for v6.1
3. Update ActiveSupport::Dependencies.constantize(lookup) to lookup.constantize
4. Add Gemfile.lock to .gitignore as we don't want to save this when doing multiple version CI

[Drew-Goddyn]

🚀