### 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 len(task_instances_list) == 2
        ti0 = (
            session.query(TaskInstance)
            .filter(TaskInstance.task_id == 'test_scheduler_verify_priority_and_slots_t0')
            .first()
        )
        assert ti0.state == State.SCHEDULED
        ti1 = (
            session.query(TaskInstance)
            .filter(TaskInstance.task_id == 'test_scheduler_verify_priority_and_slots_t1')
            .first()
        )
        assert ti1.state == State.QUEUED
        ti2 = (
            session.query(TaskInstance)
            .filter(TaskInstance.task_id == 'test_scheduler_verify_priority_and_slots_t2')
            .first()
        )
        assert ti2.state == State.QUEUED
    def test_verify_integrity_if_dag_not_changed(self, dag_maker):
        
        with create_session() as session:
            session.query(SerializedDagModel).filter(
                SerializedDagModel.dag_id == 'test_verify_integrity_if_dag_not_changed'
            ).delete(synchronize_session=False)
        with dag_maker(dag_id='test_verify_integrity_if_dag_not_changed') as dag:
            BashOperator(task_id='dummy', bash_command='echo hi')
        self.scheduler_job = SchedulerJob(subdir=os.devnull)
        session = settings.Session()
        orm_dag = dag_maker.dag_model