### 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 that tasks in removed state don't count as actively running."""
        with dag_maker(
            dag_id='test_do_schedule_max_active_runs_task_removed',
            start_date=DEFAULT_DATE,
            schedule_interval='@once',
            max_active_runs=1,
            session=session,
        ):
            
            BashOperator(task_id='dummy1', bash_command='true')
        run1 = dag_maker.create_dagrun(
            run_type=DagRunType.SCHEDULED,
            execution_date=DEFAULT_DATE + timedelta(hours=1),
            state=State.RUNNING,
        )
        self.scheduler_job = SchedulerJob(subdir=os.devnull)
        self.scheduler_job.executor = MockExecutor(do_update=False)
        self.scheduler_job.processor_agent = mock.MagicMock(spec=DagFileProcessorAgent)
        num_queued = self.scheduler_job._do_scheduling(session)
        assert num_queued == 1
        session.flush()
        ti = run1.task_instances[0]
        ti.refresh_from_db(session=session)
        assert ti.state == State.QUEUED
    def test_more_runs_are_not_created_when_max_active_runs_is_reached(self, dag_maker, caplog):