### 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
assert tis[0].state == State.SCHEDULED
            assert tis[1].state == State.SCHEDULED
    def test_scheduler_job_add_new_task(self, dag_maker):
        """
        Test if a task instance will be added if the dag is updated
        """
        with dag_maker(dag_id='test_scheduler_add_new_task') as dag:
            BashOperator(task_id='dummy', bash_command='echo test')
        self.scheduler_job = SchedulerJob(subdir=os.devnull)
        self.scheduler_job.dagbag = dag_maker.dagbag
        session = settings.Session()
        orm_dag = dag_maker.dag_model
        assert orm_dag is not None
        if self.scheduler_job.processor_agent:
            self.scheduler_job.processor_agent.end()
        self.scheduler_job = SchedulerJob(subdir=os.devnull)
        self.scheduler_job.processor_agent = mock.MagicMock()
        dag = self.scheduler_job.dagbag.get_dag('test_scheduler_add_new_task', session=session)
        self.scheduler_job._create_dag_runs([orm_dag], session)
        drs = DagRun.find(dag_id=dag.dag_id, session=session)
        assert len(drs) == 1
        dr = drs[0]
        tis = dr.get_task_instances()
        assert len(tis) == 1
        BashOperator(task_id='dummy2', dag=dag, bash_command='echo test')
        SerializedDagModel.write_dag(dag=dag)
        self.scheduler_job._schedule_dag_run(dr, session)
        assert session.query(TaskInstance).filter_by(state=State.SCHEDULED).count() == 2
        session.flush()
        drs = DagRun.find(dag_id=dag.dag_id, session=session)