remove "test/mailers" directory when skipping action-mailer

Related to #26146

railties/lib/rails/generators/rails/app/app_generator.rb

@@ -325,6 +325,7 @@ def delete_action_mailer_files_skipping_action_mailer
           remove_file "app/views/layouts/mailer.html.erb"
           remove_file "app/views/layouts/mailer.text.erb"
           remove_dir "app/mailers"
+          remove_dir "test/mailers"
         end
       end
 

railties/test/generators/app_generator_test.rb

@@ -381,6 +381,7 @@ def test_generator_if_skip_action_mailer_is_given
       assert_no_match(/config\.action_mailer/, content)
     end
     assert_no_directory "app/mailers"
+    assert_no_directory "test/mailers"
   end
 
   def test_generator_has_assets_gems