Update kube_config_test.py

fix missing method invocation

kubernetes/base/config/kube_config_test.py

@@ -1396,7 +1396,7 @@ class TestKubeConfigLoader(BaseTestCase):
                                    temp_file_path=tmp_path)
         self.assertFalse(True if not os.listdir(tmp_path) else False)
         self.assertEqual(expected, actual)
-        _cleanup_temp_files
+        _cleanup_temp_files()
 
     def test_load_kube_config_from_empty_file_like_object(self):
         config_file_like_object = io.StringIO()