### 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
[State.NONE, None, None],
            [
                State.UP_FOR_RETRY,
                timezone.utcnow() - datetime.timedelta(minutes=30),
                timezone.utcnow() - datetime.timedelta(minutes=15),
            ],
            [
                State.UP_FOR_RESCHEDULE,
                timezone.utcnow() - datetime.timedelta(minutes=30),
                timezone.utcnow() - datetime.timedelta(minutes=15),
            ],
        ],
    )
    def test_dag_file_processor_process_task_instances(self, state, start_date, end_date, dag_maker):
        """
        Test if _process_task_instances puts the right task instances into the
        mock_list.
        """
        with dag_maker(dag_id='test_scheduler_process_execute_task'):
            BashOperator(task_id='dummy', bash_command='echo hi')
        self.scheduler_job = SchedulerJob(subdir=os.devnull)
        self.scheduler_job.processor_agent = mock.MagicMock()
        dr = dag_maker.create_dagrun(run_type=DagRunType.SCHEDULED)
        assert dr is not None
        with create_session() as session:
            ti = dr.get_task_instances(session=session)[0]
            ti.state = state
            ti.start_date = start_date
            ti.end_date = end_date
            self.scheduler_job._schedule_dag_run(dr, session)