### 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
assert len(drs) == 1
        dr = drs[0]
        tis = dr.get_task_instances()
        assert len(tis) == 2
    def test_runs_respected_after_clear(self, dag_maker):
        """
        Test dag after dag.clear, max_active_runs is respected
        """
        with dag_maker(
            dag_id='test_scheduler_max_active_runs_respected_after_clear',
            start_date=DEFAULT_DATE,
            max_active_runs=1,
        ) as dag:
            BashOperator(task_id='dummy', bash_command='echo Hi')
        self.scheduler_job = SchedulerJob(subdir=os.devnull)
        self.scheduler_job.processor_agent = mock.MagicMock()
        session = settings.Session()
        dr = dag_maker.create_dagrun(run_type=DagRunType.SCHEDULED, state=State.QUEUED)
        dr = dag_maker.create_dagrun_after(dr, run_type=DagRunType.SCHEDULED, state=State.QUEUED)
        dag_maker.create_dagrun_after(dr, run_type=DagRunType.SCHEDULED, state=State.QUEUED)
        dag.clear()
        assert len(DagRun.find(dag_id=dag.dag_id, state=State.QUEUED, session=session)) == 3
        session = settings.Session()
        self.scheduler_job._start_queued_dagruns(session)
        session.flush()
        
        assert len(DagRun.find(dag_id=dag.dag_id, state=State.RUNNING, session=session)) == 1
        
        assert len(DagRun.find(dag_id=dag.dag_id, state=State.QUEUED, session=session)) == 2
    def test_timeout_triggers(self, dag_maker):