build: ignore warning from google-auth (#212)

Author: parthea

pytest.ini

@@ -15,3 +15,5 @@ filterwarnings =
     ignore:distutils Version classes are deprecated:DeprecationWarning
     # Remove once release PR https://github.com/googleapis/python-api-core/pull/555 is merged
     ignore:datetime.datetime.utcnow\(\) is deprecated:DeprecationWarning:google.api_core.datetime_helpers
+    # Remove once release PR https://github.com/googleapis/google-auth-library-python/pull/1416 is merged
+    ignore:datetime.datetime.utcnow\(\) is deprecated:DeprecationWarning:google.auth._helpers