fix: fix unit tests so they can work in g3 (#714)

* fix: mock not working well with g3 test

* update

* update
diff --git a/tests/test_impersonated_credentials.py b/tests/test_impersonated_credentials.py
index 430c770..90de704 100644
--- a/tests/test_impersonated_credentials.py
+++ b/tests/test_impersonated_credentials.py
@@ -203,7 +203,7 @@
         assert credentials.valid
         assert not credentials.expired
         # Confirm override endpoint used.
-        request_kwargs = request.call_args.kwargs
+        request_kwargs = request.call_args[1]
         assert request_kwargs["url"] == self.IAM_ENDPOINT_OVERRIDE
 
     @pytest.mark.parametrize("time_skew", [100, -100])
@@ -378,7 +378,7 @@
         assert quota_project_creds.valid
         assert not quota_project_creds.expired
         # Confirm override endpoint used.
-        request_kwargs = request.call_args.kwargs
+        request_kwargs = request.call_args[1]
         assert request_kwargs["url"] == self.IAM_ENDPOINT_OVERRIDE
 
     def test_id_token_success(