Fixed broken test from da160d440f; refs #23418.

        self.assertEqual(string, "migrations.test_writer.EmailValidator(message='hello')")

        validator = deconstructible(path="custom.EmailValidator")(EmailValidator)(message="hello")

        with self.assertRaisesMessage(ImportError, "No module named 'custom'"):

        with six.assertRaisesRegex(self, ImportError, "No module named '?custom'?"):

            MigrationWriter.serialize(validator)

        validator = deconstructible(path="django.core.validators.EmailValidator2")(EmailValidator)(message="hello")