### 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
"""
        Test to make sure executor.end gets called with a successful scheduler loop run
        """
        self.scheduler_job = SchedulerJob(subdir=os.devnull, num_runs=1)
        self.scheduler_job.executor = mock.MagicMock(slots_available=8)
        self.scheduler_job.run()
        self.scheduler_job.executor.end.assert_called_once()
        self.scheduler_job.processor_agent.end.assert_called_once()
    @mock.patch('airflow.jobs.scheduler_job.DagFileProcessorAgent')
    def test_cleanup_methods_all_called(self, mock_processor_agent):
        """
        Test to make sure all cleanup methods are called when the scheduler loop has an exception
        """
        self.scheduler_job = SchedulerJob(subdir=os.devnull, num_runs=1)
        self.scheduler_job.executor = mock.MagicMock(slots_available=8)
        self.scheduler_job._run_scheduler_loop = mock.MagicMock(side_effect=Exception("oops"))
        mock_processor_agent.return_value.end.side_effect = Exception("double oops")
        self.scheduler_job.executor.end = mock.MagicMock(side_effect=Exception("triple oops"))
        with pytest.raises(Exception):
            self.scheduler_job.run()
        self.scheduler_job.processor_agent.end.assert_called_once()
        self.scheduler_job.executor.end.assert_called_once()
        mock_processor_agent.return_value.end.reset_mock(side_effect=True)
    def test_queued_dagruns_stops_creating_when_max_active_is_reached(self, dag_maker):