chore: fix lint issues

Author: olavloite

tests/unit/spanner_dbapi/test_connect.py

@@ -139,6 +139,7 @@ def test_with_kwargs(self, mock_client):
         client = mock_client.return_value
         instance = client.instance.return_value
         database = instance.database.return_value
+        self.assertIsNotNone(database)
 
         connection = connect(INSTANCE, DATABASE, ignore_transaction_warnings=True)