### 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
run_id="test2", execution_date=DEFAULT_DATE + datetime.timedelta(seconds=1)
        )
        ti1 = dr1.get_task_instance('dummy1', session)
        ti2 = dr2.get_task_instance('dummy1', session)
        ti1.state = State.DEFERRED
        ti1.trigger_timeout = timezone.utcnow() - datetime.timedelta(seconds=60)
        ti2.state = State.DEFERRED
        ti2.trigger_timeout = timezone.utcnow() + datetime.timedelta(seconds=60)
        session.flush()
        
        self.scheduler_job = SchedulerJob(subdir=os.devnull)
        self.scheduler_job.check_trigger_timeouts(session=session)
        
        session.refresh(ti1)
        session.refresh(ti2)
        assert ti1.state == State.SCHEDULED
        assert ti1.next_method == "__fail__"
        assert ti2.state == State.DEFERRED
@pytest.mark.xfail(reason="Work out where this goes")
def test_task_with_upstream_skip_process_task_instances():
    """
    Test if _process_task_instances puts a task instance into SKIPPED state if any of its
    upstream tasks are skipped according to TriggerRuleDep.
    """
    clear_db_runs()
    with DAG(
        dag_id='test_task_with_upstream_skip_dag', start_date=DEFAULT_DATE, schedule_interval=None
    ) as dag:
        dummy1 = DummyOperator(task_id='dummy1')
        dummy2 = DummyOperator(task_id="dummy2")