### 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=dag, start_date=start_date, end_date=end_date, executor=executor, donot_pickle=True
                )
                job.run()
        backfill_job_thread = threading.Thread(
            target=run_backfill, name="run_backfill", args=(dag_run_created_cond,)
        )
        dag_run_created_cond.acquire()
        with create_session() as session:
            backfill_job_thread.start()
            try:
                
                
                dag_run_created_cond.wait(timeout=1.5)
                dagruns = DagRun.find(dag_id=dag_id)
                assert 1 == len(dagruns)
                dr = dagruns[0]
                assert dr.run_id == run_id
                
                
                
                dr.set_state(State.SUCCESS)
                session.merge(dr)
                session.commit()
                backfill_job_thread.join()
                dagruns = DagRun.find(dag_id=dag_id)
                assert 3 == len(dagruns)  
                assert dagruns[-1].run_id == dr.run_id
            finally:
                dag_run_created_cond.release()
    def test_backfill_max_limit_check_no_count_existing(self, dag_maker):