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_iam.py b/tests/test_iam.py
index fbd3e41..382713b 100644
--- a/tests/test_iam.py
+++ b/tests/test_iam.py
@@ -89,7 +89,7 @@
         returned_signature = signer.sign("123")
 
         assert returned_signature == signature
-        kwargs = request.call_args.kwargs
+        kwargs = request.call_args[1]
         assert kwargs["headers"]["Content-Type"] == "application/json"
 
     def test_sign_bytes_failure(self):