activestorage: Attached::Many should support methods of ActiveRerord

[tk0miya]

ActiveStorage::Attached::Many delegates missing method calls to the ActiveRecord::Relation object; #attachments. Therefore it should support methods of AR::Relation.

refs:

• https://github.com/rails/rails/blob/v7.1.0/activestorage/lib/active_storage/attached/many.rb#L27
• https://github.com/rails/rails/blob/v7.1.0/activestorage/lib/active_storage/attached/model.rb#L201