### 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 task instances not queued when pool is full.
        Variation with non-default pool_slots
        """
        with dag_maker(
            dag_id='test_scheduler_verify_pool_full_2_slots_per_task',
            start_date=DEFAULT_DATE,
            session=session,
        ):
            BashOperator(
                task_id='dummy',
                pool='test_scheduler_verify_pool_full_2_slots_per_task',
                pool_slots=2,
                bash_command='echo hi',
            )
        pool = Pool(pool='test_scheduler_verify_pool_full_2_slots_per_task', slots=6)
        session.add(pool)
        session.flush()
        self.scheduler_job = SchedulerJob(executor=self.null_exec)
        self.scheduler_job.processor_agent = mock.MagicMock()
        
        def _create_dagruns():