fix: Added missing import into logger.py (#896)

Author: gkevinzheng

google/cloud/logging_v2/logger.py

@@ -29,6 +29,7 @@
 from google.api_core.exceptions import InvalidArgument
 from google.rpc.error_details_pb2 import DebugInfo
 
+import google.cloud.logging_v2
 import google.protobuf.message
 
 _GLOBAL_RESOURCE = Resource(type="global", labels={})