[Serializer] Fixed serialize and denormalize return types

src/Symfony/Component/Serializer/Normalizer/DenormalizerInterface.php

@@ -32,7 +32,7 @@ interface DenormalizerInterface
      * @param string $format  Format the given data was extracted from
      * @param array  $context Options available to the denormalizer
      *
-     * @return object|array
+     * @return mixed
      *
      * @throws BadMethodCallException   Occurs when the normalizer is not called in an expected context
      * @throws InvalidArgumentException Occurs when the arguments are not coherent or not supported

src/Symfony/Component/Serializer/SerializerInterface.php

@@ -32,7 +32,7 @@ interface SerializerInterface
      *
      * @param mixed $data
      *
-     * @return object|array
+     * @return mixed
      */
     public function deserialize($data, string $type, string $format, array $context = []);
 }