Fix pickyness of google.auth 2.36.0 for mocks (apache#43771)

Google-auth 2.36.0 is more picky about credentials being mocked. It
expects the `universe_domain` attribute to be real string not
mock because it passes it as argument of `replace` string method.

providers/tests/google/common/hooks/test_base_google.py

@@ -1022,6 +1022,7 @@ async def test_get_token(self, mock_auth_default, monkeypatch) -> None:
     async def test_get_token_impersonation(self, mock_auth_default, monkeypatch, requests_mock) -> None:
         mock_credentials = mock.MagicMock(spec=google.auth.compute_engine.Credentials)
         mock_credentials.token = "ACCESS_TOKEN"
+        mock_credentials.universe_domain = "googleapis.com"
         mock_auth_default.return_value = (mock_credentials, "PROJECT_ID")
         monkeypatch.setenv(
             "AIRFLOW_CONN_GOOGLE_CLOUD_DEFAULT",
@@ -1045,6 +1046,7 @@ async def test_get_token_impersonation(self, mock_auth_default, monkeypatch, req
     @mock.patch("google.auth.default")
     async def test_get_token_impersonation_conn(self, mock_auth_default, monkeypatch, requests_mock) -> None:
         mock_credentials = mock.MagicMock(spec=google.auth.compute_engine.Credentials)
+        mock_credentials.universe_domain = "googleapis.com"
         mock_auth_default.return_value = (mock_credentials, "PROJECT_ID")
         monkeypatch.setenv(
             "AIRFLOW_CONN_GOOGLE_CLOUD_DEFAULT",