[Python 3] Fixed the issue processing the request data (decoding issue)

for UPDATE operation of the server node.

web/pgadmin/browser/server_groups/servers/__init__.py

@@ -317,7 +317,7 @@ class ServerNode(PGChildNodeView):
         }
 
         idx = 0
-        data = request.form if request.form else json.loads(request.data)
+        data = request.form if request.form else json.loads(request.data.decode())
 
         from pgadmin.utils.driver import get_driver
         manager = get_driver(PG_DEFAULT_DRIVER).connection_manager(sid)