fix(celery): don't use msgpack serializer due to problems with certain data types

rhodecode/lib/celerylib/loader.py

@@ -72,9 +72,9 b' base_celery_config = {'
     'worker_max_tasks_per_child': 100,
     'worker_hijack_root_logger': False,
     'worker_prefetch_multiplier': 1,
-    'task_serializer': 'msgpack',
+    'task_serializer': 'json',
     'accept_content': ['json', 'msgpack'],
-    'result_serializer': 'msgpack',
+    'result_serializer': 'json',
     'result_accept_content': ['json', 'msgpack'],
 
     'broker_connection_retry_on_startup': True,