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/oauth2/test_service_account.py b/tests/oauth2/test_service_account.py
index 40a4ca2..648541e 100644
--- a/tests/oauth2/test_service_account.py
+++ b/tests/oauth2/test_service_account.py
@@ -203,18 +203,18 @@
         assert "x-goog-user-project" not in headers
         assert "token" in headers["authorization"]
 
-    @mock.patch("google.auth.jwt.Credentials.from_signing_credentials", autospec=True)
-    def test__create_self_signed_jwt(self, from_signing_credentials):
+    @mock.patch("google.auth.jwt.Credentials", instance=True, autospec=True)
+    def test__create_self_signed_jwt(self, jwt):
         credentials = service_account.Credentials(
             SIGNER, self.SERVICE_ACCOUNT_EMAIL, self.TOKEN_URI
         )
 
         audience = "https://pubsub.googleapis.com"
         credentials._create_self_signed_jwt(audience)
-        from_signing_credentials.assert_called_once_with(credentials, audience)
+        jwt.from_signing_credentials.assert_called_once_with(credentials, audience)
 
-    @mock.patch("google.auth.jwt.Credentials.from_signing_credentials", autospec=True)
-    def test__create_self_signed_jwt_with_user_scopes(self, from_signing_credentials):
+    @mock.patch("google.auth.jwt.Credentials", instance=True, autospec=True)
+    def test__create_self_signed_jwt_with_user_scopes(self, jwt):
         credentials = service_account.Credentials(
             SIGNER, self.SERVICE_ACCOUNT_EMAIL, self.TOKEN_URI, scopes=["foo"]
         )
@@ -223,7 +223,7 @@
         credentials._create_self_signed_jwt(audience)
 
         # JWT should not be created if there are user-defined scopes
-        from_signing_credentials.assert_not_called()
+        jwt.from_signing_credentials.assert_not_called()
 
     @mock.patch("google.oauth2._client.jwt_grant", autospec=True)
     def test_refresh_success(self, jwt_grant):
diff --git a/tests/oauth2/test_sts.py b/tests/oauth2/test_sts.py
index 8792bd6..e8e008d 100644
--- a/tests/oauth2/test_sts.py
+++ b/tests/oauth2/test_sts.py
@@ -128,7 +128,7 @@
             self.ADDON_HEADERS,
         )
 
-        self.assert_request_kwargs(request.call_args.kwargs, headers, request_data)
+        self.assert_request_kwargs(request.call_args[1], headers, request_data)
         assert response == self.SUCCESS_RESPONSE
 
     def test_exchange_token_partial_success_without_auth(self):
@@ -157,7 +157,7 @@
             requested_token_type=self.REQUESTED_TOKEN_TYPE,
         )
 
-        self.assert_request_kwargs(request.call_args.kwargs, headers, request_data)
+        self.assert_request_kwargs(request.call_args[1], headers, request_data)
         assert response == self.SUCCESS_RESPONSE
 
     def test_exchange_token_non200_without_auth(self):
@@ -227,7 +227,7 @@
             self.ADDON_HEADERS,
         )
 
-        self.assert_request_kwargs(request.call_args.kwargs, headers, request_data)
+        self.assert_request_kwargs(request.call_args[1], headers, request_data)
         assert response == self.SUCCESS_RESPONSE
 
     def test_exchange_token_partial_success_with_basic_auth(self):
@@ -259,7 +259,7 @@
             requested_token_type=self.REQUESTED_TOKEN_TYPE,
         )
 
-        self.assert_request_kwargs(request.call_args.kwargs, headers, request_data)
+        self.assert_request_kwargs(request.call_args[1], headers, request_data)
         assert response == self.SUCCESS_RESPONSE
 
     def test_exchange_token_non200_with_basic_auth(self):
@@ -331,7 +331,7 @@
             self.ADDON_HEADERS,
         )
 
-        self.assert_request_kwargs(request.call_args.kwargs, headers, request_data)
+        self.assert_request_kwargs(request.call_args[1], headers, request_data)
         assert response == self.SUCCESS_RESPONSE
 
     def test_exchange_token_partial_success_with_reqbody_auth(self):
@@ -362,7 +362,7 @@
             requested_token_type=self.REQUESTED_TOKEN_TYPE,
         )
 
-        self.assert_request_kwargs(request.call_args.kwargs, headers, request_data)
+        self.assert_request_kwargs(request.call_args[1], headers, request_data)
         assert response == self.SUCCESS_RESPONSE
 
     def test_exchange_token_non200_with_reqbody_auth(self):