Import Literal from typing_extensions to support older Python versions

Author: rnestler

asyncua/common/connection.py

@@ -3,7 +3,7 @@
 from datetime import datetime, timedelta
 import logging
 import copy
-from typing import Literal
+from typing_extensions import Literal
 
 from asyncua import ua
 from asyncua.ua.uaerrors import UaInvalidParameterError