### 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='dummy')
        self.scheduler_job = SchedulerJob(subdir=os.devnull)
        self.scheduler_job.executor = MockExecutor()
        self.scheduler_job.processor_agent = mock.MagicMock(spec=DagFileProcessorAgent)
        self.scheduler_job._create_dag_runs([dag_maker.dag_model], session)
        self.scheduler_job._start_queued_dagruns(session)
        
        dr = DagRun.find(execution_date=DEFAULT_DATE, session=session)[0]
        ti = dr.get_task_instance(task_id='dummy')
        ti.state = State.SUCCESS
        session.merge(ti)
        session.flush()
        self.scheduler_job._schedule_dag_run(dr, session)
        session.flush()
        
        self.scheduler_job._schedule_dag_run(dr, session)
        session.flush()
        dag.catchup = False
        dag.sync_to_db()
        assert not dag.catchup
        dm = DagModel.get_dagmodel(dag.dag_id)
        self.scheduler_job._create_dag_runs([dm], session)
        
        
        assert (
            session.query(DagRun.execution_date)
            .filter(DagRun.execution_date != DEFAULT_DATE)  
            .scalar()
        ) > (timezone.utcnow() - timedelta(days=2))