### 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
BashOperator(task_id='task', bash_command='true')
        self.scheduler_job = SchedulerJob(subdir=os.devnull)
        self.scheduler_job.executor = MockExecutor(do_update=True)
        self.scheduler_job.processor_agent = mock.MagicMock(spec=DagFileProcessorAgent)
        DagModel.dags_needing_dagruns(session).all()
        for _ in range(3):
            self.scheduler_job._do_scheduling(session)
        model: DagModel = session.query(DagModel).get(dag.dag_id)
        
        assert DagRun.active_runs_of_dags(session=session) == {'test_dag': 3}
        assert model.next_dagrun == timezone.convert_to_utc(
            timezone.DateTime(
                2016,
                1,
                3,
            )
        )
        assert model.next_dagrun_create_after is None
        complete_one_dagrun()
        assert DagRun.active_runs_of_dags(session=session) == {'test_dag': 3}
        for _ in range(5):
            self.scheduler_job._do_scheduling(session)
            complete_one_dagrun()
            model: DagModel = session.query(DagModel).get(dag.dag_id)
        expected_execution_dates = [datetime.datetime(2016, 1, d, tzinfo=timezone.utc) for d in range(1, 6)]
        dagrun_execution_dates = [
            dr.execution_date for dr in session.query(DagRun).order_by(DagRun.execution_date).all()
        ]
        assert dagrun_execution_dates == expected_execution_dates
    def test_do_schedule_max_active_runs_and_manual_trigger(self, dag_maker):