### 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
max_active_tis_per_dag = 2
        dag = self._get_dummy_dag(
            dag_maker,
            dag_id='test_backfill_respect_max_active_tis_per_dag_limit',
            max_active_tis_per_dag=max_active_tis_per_dag,
        )
        dag_maker.create_dagrun()
        executor = MockExecutor()
        job = BackfillJob(
            dag=dag,
            executor=executor,
            start_date=DEFAULT_DATE,
            end_date=DEFAULT_DATE + datetime.timedelta(days=7),
        )
        job.run()
        assert len(executor.history) > 0
        task_concurrency_limit_reached_at_least_once = False
        num_running_task_instances = 0
        for running_task_instances in executor.history:
            assert len(running_task_instances) <= max_active_tis_per_dag