### 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
self.scheduler_job = SchedulerJob(num_runs=1, executor=executor, subdir=os.devnull)
            self.scheduler_job.dagbag = dag_maker.dagbag
            self.scheduler_job.heartrate = 0
            
            
            with mock.patch.object(DagModel, "deactivate_deleted_dags"):
                self.scheduler_job.run()
        do_schedule()
        with create_session() as session:
            ti = (
                session.query(TaskInstance)
                .filter(
                    TaskInstance.dag_id == 'test_retry_still_in_executor',
                    TaskInstance.task_id == 'test_retry_handling_op',
                )
                .first()
            )
        assert ti is not None, "Task not created by scheduler"
        ti.task = dag_task1
        def run_with_error(ti, ignore_ti_state=False):