Merge pull request #15548 from zuhao/refactor_actionmailer_i18n_with_controller_test

Restore I18n.locale to default after test.

actionmailer/test/i18n_with_controller_test.rb

@@ -32,6 +32,10 @@ def app
     Routes
   end
 
+  teardown do
+    I18n.locale = I18n.default_locale
+  end
+
   def test_send_mail
     with_translation 'de', email_subject: '[Anmeldung] Willkommen' do
       get '/test/send_mail'