fix(vcsserver): make serializer consistent like in rhodecode

vcsserver/hooks.py

@@ -95,9 +95,9 b' class HooksCeleryClient:'
         celery_app.config_from_object({
             'broker_url': queue, 'result_backend': backend,
             'broker_connection_retry_on_startup': True,
-            'task_serializer': 'msgpack',
+            'task_serializer': 'json',
             'accept_content': ['json', 'msgpack'],
-            'result_serializer': 'msgpack',
+            'result_serializer': 'json',
             'result_accept_content': ['json', 'msgpack']
         })
         self.celery_app = celery_app