### 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
dr.state == DagRunState.QUEUED
        assert session.query(DagRun).count() == 1
        assert dag_maker.dag_model.next_dagrun_create_after is None
        session.flush()
        
        assert len(DagModel.dags_needing_dagruns(session).all()) == 0
        self.scheduler_job._create_dag_runs(dag_models, session)
        assert session.query(DagRun).count() == 1
        assert dag_maker.dag_model.next_dagrun_create_after is None
        assert dag_maker.dag_model.next_dagrun == DEFAULT_DATE
        
        dr = session.query(DagRun).one()
        dr.state = DagRunState.SUCCESS
        ti = dr.get_task_instance('task', session)
        ti.state = TaskInstanceState.SUCCESS
        session.merge(ti)
        session.merge(dr)
        session.flush()
        
        self.scheduler_job._schedule_dag_run(dr, session)
        session.flush()
        assert len(DagModel.dags_needing_dagruns(session).all()) == 1
        
        assert dag_maker.dag_model.next_dagrun == DEFAULT_DATE + timedelta(days=1)
        
        assert (
            session.query(DagRun).filter(DagRun.state.in_([DagRunState.RUNNING, DagRunState.QUEUED])).count()
            == 0
        )
    def test_max_active_runs_creation_phasing(self, dag_maker, session):