### 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
run1_ti = run1.get_task_instance(task1.task_id, session)
        run1_ti.state = State.RUNNING
        run2 = dag.create_dagrun(
            run_type=DagRunType.SCHEDULED,
            execution_date=DEFAULT_DATE + timedelta(seconds=10),
            state=State.QUEUED,
            session=session,
        )
        self.scheduler_job = SchedulerJob(subdir=os.devnull)
        self.scheduler_job.executor = MockExecutor()
        self.scheduler_job.processor_agent = mock.MagicMock(spec=DagFileProcessorAgent)
        my_dag = session.query(DagModel).get(dag.dag_id)
        self.scheduler_job._create_dag_runs([my_dag], session)
        
        self.scheduler_job._schedule_dag_run(run1, session)
        run1 = session.merge(run1)
        session.refresh(run1)
        assert run1.state == State.FAILED
        assert run1_ti.state == State.SKIPPED
        session.flush()
        
        self.scheduler_job._start_queued_dagruns(session)
        session.flush()
        run2 = session.merge(run2)
        session.refresh(run2)
        assert run2.state == State.RUNNING
        self.scheduler_job._schedule_dag_run(run2, session)
        run2_ti = run2.get_task_instance(task1.task_id, session)
        assert run2_ti.state == State.SCHEDULED
    def test_do_schedule_max_active_runs_task_removed(self, session, dag_maker):