### Body

Add unit test for changes in https://github.com/apache/airflow/pull/17305

### Committer

- [X] I acknowledge that I am a maintainer/committer of the Apache Airflow project.
tests/jobs/test_backfill_job.py
with dag_maker(
            'test_sub_set_subdag',
        ) as dag:
            op1 = DummyOperator(task_id='leave1')
            op2 = DummyOperator(task_id='leave2')
            op3 = DummyOperator(task_id='upstream_level_1')
            op4 = DummyOperator(task_id='upstream_level_2')
            op5 = DummyOperator(task_id='upstream_level_3')
            
            op2.set_downstream(op3)
            op1.set_downstream(op3)
            op4.set_downstream(op5)
            op3.set_downstream(op4)
        dr = dag_maker.create_dagrun()
        executor = MockExecutor()
        sub_dag = dag.partial_subset(
            task_ids_or_regex="leave*", include_downstream=False, include_upstream=False
        )
        job = BackfillJob(dag=sub_dag, start_date=DEFAULT_DATE, end_date=DEFAULT_DATE, executor=executor)
        job.run()
        for ti in dr.get_task_instances():
            if ti.task_id == 'leave1' or ti.task_id == 'leave2':
                assert State.SUCCESS == ti.state
            else:
                assert State.NONE == ti.state
    def test_backfill_fill_blanks(self, dag_maker):