### 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
"""
        Test if a a dagrun will not be scheduled if max_dag_runs
        has been reached and dagrun_timeout is not reached
        Test if a a dagrun would be scheduled if max_dag_runs has
        been reached but dagrun_timeout is also reached
        """
        with dag_maker(
            dag_id='test_scheduler_verify_max_active_runs_and_dagrun_timeout',
            start_date=DEFAULT_DATE,
            max_active_runs=1,
            dagrun_timeout=datetime.timedelta(seconds=60),
        ) as dag:
            DummyOperator(task_id='dummy')
        self.scheduler_job = SchedulerJob(subdir=os.devnull)
        self.scheduler_job.dagbag = dag_maker.dagbag
        session = settings.Session()
        orm_dag = session.query(DagModel).get(dag.dag_id)
        assert orm_dag is not None
        self.scheduler_job._create_dag_runs([orm_dag], session)
        self.scheduler_job._start_queued_dagruns(session)
        drs = DagRun.find(dag_id=dag.dag_id, session=session)
        assert len(drs) == 1
        dr = drs[0]
        assert orm_dag.next_dagrun_create_after is None
        
        assert isinstance(orm_dag.next_dagrun, datetime.datetime)
        assert isinstance(orm_dag.next_dagrun_data_interval_start, datetime.datetime)