Merge branch '3.4' into 4.4

* 3.4:
  switch the context when validating nested forms
  Fix typo
  [HttpKernel] Fix regression where Store does not return response body correctly
  rework form validator tests
  Update AbstractController.php

Author: nicolas-grekas

Controller/ControllerTrait.php

@@ -156,7 +156,7 @@ protected function file($file, string $fileName = null, string $disposition = Re
      *
      * @final
      */
-    protected function addFlash(string $type, string $message)
+    protected function addFlash(string $type, $message)
     {
         if (!$this->container->has('session')) {
             throw new \LogicException('You can not use the addFlash method if sessions are disabled. Enable them in "config/packages/framework.yaml".');