fix: add 'type: ignore' comment for 'google.auth' (#579)

Author: tseaver

gapic/templates/%namespace/%name_%version/%sub/services/%service/transports/base.py.j2

@@ -5,7 +5,7 @@ import abc
 import typing
 import pkg_resources
 
-from google import auth
+from google import auth  # type: ignore
 from google.api_core import exceptions  # type: ignore
 from google.api_core import gapic_v1    # type: ignore
 from google.api_core import retry as retries  # type: ignore