### 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
dag = self._get_dag_test_max_active_limits(
            dag_maker, dag_id='test_backfill_max_limit_check_complete_loop'
        )
        dag_maker.create_dagrun()
        start_date = DEFAULT_DATE - datetime.timedelta(hours=1)
        end_date = DEFAULT_DATE
        
        
        success_expected = 2
        executor = MockExecutor()
        job = BackfillJob(
            dag=dag, start_date=start_date, end_date=end_date, executor=executor, donot_pickle=True
        )
        job.run()
        success_dagruns = len(DagRun.find(dag_id=dag.dag_id, state=State.SUCCESS))
        running_dagruns = len(DagRun.find(dag_id=dag.dag_id, state=State.RUNNING))
        assert success_expected == success_dagruns
        assert 0 == running_dagruns  
    def test_sub_set_subdag(self, dag_maker):