Add missing conflict with symfony/serializer <4.4

Author: yceruto

composer.json

@@ -79,7 +79,7 @@
         "symfony/mime": "<4.4",
         "symfony/property-info": "<3.4",
         "symfony/security-bundle": "<4.4",
-        "symfony/serializer": "<4.2",
+        "symfony/serializer": "<4.4",
         "symfony/stopwatch": "<3.4",
         "symfony/translation": "<4.4",
         "symfony/twig-bridge": "<4.1.1",