We were getting a deprecation warning in the logs after upgrading to Rails 7.1: ``` DEPRECATION WARNING: Using preview_path= option is deprecated and will be removed in Rails 7.2. Please use preview_paths= instead. ``` So we're appending a path to the `preview_paths`, as recommended in the guide to upgrade to Rails 7.1 [1]. [1] https://guides.rubyonrails.org/v7.1/upgrading_ruby_on_rails.html#support-multiple-preview-paths-for-actionmailer-preview