### 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
if advance_execution_date:
            
            dr = dag.create_dagrun(
                run_type=DagRunType.SCHEDULED,
                execution_date=dr.data_interval_end,
                state=State.RUNNING,
                session=session,
            )
        ex_date = dr.execution_date
        for tid, state in expected_task_states.items():
            if state != State.FAILED:
                continue
            self.null_exec.mock_task_fail(dag_id, tid, dr.run_id)
        try:
            dag = DagBag().get_dag(dag.dag_id)
            assert not isinstance(dag, SerializedDAG)
            
            dag.run(start_date=ex_date, end_date=ex_date, executor=self.null_exec, **run_kwargs)
        except AirflowException:
            pass
        
        dr = DagRun.find(dag_id=dag_id, execution_date=ex_date, session=session)
        dr = dr[0]
        dr.dag = dag
        assert dr.state == dagrun_state
        
        for task_id, expected_state in expected_task_states.items():
            ti = dr.get_task_instance(task_id)
            assert ti.state == expected_state
    def test_dagrun_fail(self):