### Body

The `test_no_orphan_process_will_be_left` in `TestSchedulerJob` is really flaky.

Before we know how to fix it, I will quarantine it:

https://github.com/apache/airflow/pull/18691/checks?check_run_id=3811660138

```
  =================================== FAILURES ===================================
  _____________ TestSchedulerJob.test_no_orphan_process_will_be_left _____________
  
  self = <tests.jobs.test_scheduler_job.TestSchedulerJob object at 0x7fc2f91d2ac8>
  
      def test_no_orphan_process_will_be_left(self):
          empty_dir = mkdtemp()
          current_process = psutil.Process()
          old_children = current_process.children(recursive=True)
          self.scheduler_job = SchedulerJob(
              subdir=empty_dir, num_runs=1, executor=MockExecutor(do_update=False)
          )
          self.scheduler_job.run()
          shutil.rmtree(empty_dir)
      
          # Remove potential noise created by previous tests.
          current_children = set(current_process.children(recursive=True)) - set(old_children)
  >       assert not current_children
  E       AssertionError: assert not {psutil.Process(pid=2895, name='pytest', status='running', started='06:53:45')}
  
```

### Committer

- [X] I acknowledge that I am a maintainer/committer of the Apache Airflow project.
tests/jobs/test_scheduler_job.py
session = settings.Session()
        with dag_maker('test_dag1', max_active_runs=1) as dag:
            DummyOperator(task_id='mytask')
        date = dag.following_schedule(DEFAULT_DATE)
        for i in range(30):
            dr = dag_maker.create_dagrun(
                run_id=f'dagrun_{i}', run_type=DagRunType.SCHEDULED, state=State.QUEUED, execution_date=date
            )
            date = dr.execution_date + timedelta(hours=1)
        self.scheduler_job = SchedulerJob(subdir=os.devnull)
        self.scheduler_job.executor = MockExecutor(do_update=False)
        self.scheduler_job.processor_agent = mock.MagicMock(spec=DagFileProcessorAgent)
        self.scheduler_job._start_queued_dagruns(session)
        session.flush()
        dr = DagRun.find(run_id='dagrun_0')
        ti = dr[0].get_task_instance(task_id='mytask', session=session)
        ti.state = State.SUCCESS
        session.merge(ti)
        session.commit()
        assert dr[0].state == State.RUNNING
        dr[0].state = State.SUCCESS
        session.merge(dr[0])
        session.flush()
        assert dr[0].state == State.SUCCESS
        self.scheduler_job._start_queued_dagruns(session)
        session.flush()
        dr = DagRun.find(run_id='dagrun_1')
        assert len(session.query(DagRun).filter(DagRun.state == State.RUNNING).all()) == 1
        assert dr[0].state == State.RUNNING
    def test_no_dagruns_would_stuck_in_running(self, dag_maker):