Support Rails 7.2

[ajvondrak]

• Bumped the gemspec to permit Rails 7.2.x
• Required an update to the tests because ActiveRecord::Base.connection was deprecated in favor of ActiveRecord::Base.lease_connection and ActiveRecord::Base.with_connection: PoC: Add an option to disable connection checkout caching rails/rails#50793
• The actual gem code doesn't call ActiveRecord::Base.connection, it's just used in test assertions
• Confirmed the tests pass under Rails 7.2.2.1 locally

[isnotajoke]

Looks similar to a prior PR doing something similar. I also looked through the gem code to confirm that nothing seemed to be relying on the changed method outside of specs (as noted in the description). Seems safe to me.