Merge branch '5.4' into 6.2

* 5.4:
  [Validator] add missing German translations
  [Serializer] Fix denormalizing abstract part headers in MimeMessageNormalizer
  [Form] Remove an obsolete phpdoc comment
  [FrameworkBundle][Workflow] Throw exception is workflow.xxx.transitions is not an array

Author: nicolas-grekas

Normalizer/MimeMessageNormalizer.php

@@ -86,6 +86,7 @@ public function denormalize(mixed $data, string $type, string $format = null, ar
         if (AbstractPart::class === $type) {
             $type = $data['class'];
             unset($data['class']);
+            $data['headers'] = $this->serializer->denormalize($data['headers'], Headers::class, $format, $context);
         }
 
         return $this->normalizer->denormalize($data, $type, $format, $context);