### 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.dagbag.get_dag('example_subdag_operator')
        subdag_op_task = dag.get_task('section-1')
        subdag = subdag_op_task.subdag
        subdag.timetable = cron_timetable('@daily')
        start_date = timezone.utcnow()
        executor = MockExecutor()
        job = BackfillJob(
            dag=subdag, start_date=start_date, end_date=start_date, executor=executor, donot_pickle=True
        )
        job.run()
        subdag_op_task.pre_execute(context={'execution_date': start_date})
        subdag_op_task.execute(context={'execution_date': start_date})
        subdag_op_task.post_execute(context={'execution_date': start_date})
        history = executor.history
        subdag_history = history[0]
        
        assert 5 == len(subdag_history)
        for sdh in subdag_history:
            ti = sdh[3]
            assert 'section-1-task-' in ti.task_id
        with create_session() as session:
            successful_subdag_runs = (