### 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
task_callback = mock.MagicMock()
        mock_task_callback.return_value = task_callback
        self.scheduler_job = SchedulerJob(executor=executor)
        self.scheduler_job.processor_agent = mock.MagicMock()
        ti1.state = State.QUEUED
        session.merge(ti1)
        session.commit()
        executor.event_buffer[ti1.key] = State.FAILED, None
        self.scheduler_job._process_executor_events(session=session)
        ti1.refresh_from_db(session=session)
        assert ti1.state == State.UP_FOR_RETRY
        self.scheduler_job.processor_agent.send_callback_to_execute.assert_not_called()
        self.scheduler_job.processor_agent.reset_mock()
        
        ti1.state = State.SUCCESS
        session.merge(ti1)
        session.commit()
        executor.event_buffer[ti1.key] = State.SUCCESS, None
        self.scheduler_job._process_executor_events(session=session)
        ti1.refresh_from_db(session=session)
        assert ti1.state == State.SUCCESS
        self.scheduler_job.processor_agent.send_callback_to_execute.assert_not_called()
        mock_stats_incr.assert_has_calls(
            [
                mock.call('scheduler.tasks.killed_externally'),
                mock.call('operator_failures_DummyOperator', 1, 1),
                mock.call('ti_failures'),
            ],
            any_order=True,
        )