Ensure that this works:

```python
@setup
def mytask():
    print("I am a setup task")

with dag_maker() as dag:
    mytask.override(task_id='newtask')

assert len(dag.task_group.children) == 1
setup_task = dag.task_group.children["newtask"]
assert setup_task._is_setup
```
and teardown also works
"""Verify a timetable-backed schedule_interval is excluded in serialization."""
        dag = get_timetable_based_simple_dag(timetable)
        serialized_dag = SerializedDAG.to_dict(dag)
        SerializedDAG.validate_schema(serialized_dag)
        expected = copy.deepcopy(serialized_simple_dag_ground_truth)
        del expected["dag"]["schedule_interval"]
        expected["dag"]["timetable"] = serialized_timetable
        self.validate_serialized_dag(serialized_dag, expected)
    def test_dag_serialization_unregistered_custom_timetable(self):