Follow instructions and set legacy_connection_handling to false

Author: petergoldstein

example_app_generator/spec/support/default_preview_path

@@ -48,6 +48,8 @@ require_file_stub 'config/environment' do
         if ENV['SHOW_PREVIEWS']
           config.action_mailer.show_previews = (ENV['SHOW_PREVIEWS'] == 'true')
         end
+
+        config.legacy_connection_handling = false if Rails::VERSION::STRING >= '7'
       end
     end