### 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
):
            DummyOperator(task_id='mytask')
        dr = dag_maker.create_dagrun(run_type=DagRunType.SCHEDULED, state=State.QUEUED)
        for _ in range(29):
            dr = dag_maker.create_dagrun_after(dr, run_type=DagRunType.SCHEDULED, state=State.QUEUED)
        with dag_maker(
            'test_dag2',
            start_date=timezone.datetime(2020, 1, 1),
            schedule_interval=timedelta(hours=1),
        ):
            DummyOperator(task_id='mytask')
        dr = dag_maker.create_dagrun(run_type=DagRunType.SCHEDULED, state=State.QUEUED)
        for _ in range(9):
            dr = dag_maker.create_dagrun_after(dr, run_type=DagRunType.SCHEDULED, state=State.QUEUED)
        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()
        self.scheduler_job._start_queued_dagruns(session)
        session.flush()
        dag1_running_count = (
            session.query(func.count(DagRun.id))
            .filter(DagRun.dag_id == "test_dag1", DagRun.state == State.RUNNING)
            .scalar()
        )
        running_count = session.query(func.count(DagRun.id)).filter(DagRun.state == State.RUNNING).scalar()
        assert dag1_running_count == 1
        assert running_count == 11
    def test_start_queued_dagruns_do_follow_execution_date_order(self, dag_maker):