Merge branch '5.4' into 6.3

* 5.4:
  [Form] Fix merging params & files when "multiple" is enabled
  [HttpFoundation] Do not swallow trailing `=` in cookie value
  Handle Sendinblue error responses without a message key
  [Serializer] Fix collecting only first missing constructor argument
  [Messenger] Fix DoctrineOpenTransactionLoggerMiddleware
  [Translation] Add missing return type
  [Validator] add missing catalan translations

Util/ArrayConverter.php

@@ -96,7 +96,10 @@ private static function cancelExpand(array &$tree, string $prefix, array $node):
         }
     }
 
-    private static function getKeyParts(string $key)
+    /**
+     * @return string[]
+     */
+    private static function getKeyParts(string $key): array
     {
         $parts = explode('.', $key);
         $partsCount = \count($parts);