### 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
scheduler.processor_agent = mock.MagicMock()
        def _create_dagruns(dag: DAG):
            next_info = dag.next_dagrun_info(None)
            assert next_info is not None
            for _ in range(5):
                yield dag.create_dagrun(
                    run_type=DagRunType.SCHEDULED,
                    execution_date=next_info.logical_date,
                    data_interval=next_info.data_interval,
                    state=State.RUNNING,
                )
                next_info = dag.next_dagrun_info(next_info.data_interval)
                if next_info is None:
                    break
        
        
        
        for dr in _create_dagruns(dag_d1):
            scheduler._schedule_dag_run(dr, session)
        for dr in _create_dagruns(dag_d2):
            scheduler._schedule_dag_run(dr, session)
        scheduler._executable_task_instances_to_queued(max_tis=2, session=session)
        task_instances_list2 = scheduler._executable_task_instances_to_queued(max_tis=2, session=session)
        
        assert len(task_instances_list2) > 0
        assert all(
            task_instance.pool != 'test_scheduler_keeps_scheduling_pool_full_p1'
            for task_instance in task_instances_list2
        )
    def test_scheduler_verify_priority_and_slots(self, dag_maker):