### 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
dagruns = []
            dagbag = DagBag(dag_folder=ELASTIC_DAG_FILE, include_examples=False, read_dags_from_db=False)
            dagbag.sync_to_db()
            dag_ids = dagbag.dag_ids
            dagbag = DagBag(read_dags_from_db=True)
            for i, dag_id in enumerate(dag_ids):
                dag = dagbag.get_dag(dag_id)
                dr = dag.create_dagrun(
                    state=State.RUNNING,
                    run_id=f"{DagRunType.MANUAL.value}__{i}",
                    dag_hash=dagbag.dags_hash[dag.dag_id],
                )
                dagruns.append(dr)
                for ti in dr.get_task_instances():
                    ti.set_state(state=State.SCHEDULED)
            mock_agent = mock.MagicMock()
            self.scheduler_job = SchedulerJob(subdir=PERF_DAGS_FOLDER, num_runs=1)
            self.scheduler_job.executor = MockExecutor(do_update=False)
            self.scheduler_job.heartbeat = mock.MagicMock()
            self.scheduler_job.processor_agent = mock_agent
            with assert_queries_count(expected_query_count):
                with mock.patch.object(DagRun, 'next_dagruns_to_examine') as mock_dagruns:
                    mock_dagruns.return_value = dagruns
                    self.scheduler_job._run_scheduler_loop()
    @pytest.mark.parametrize(
        "expected_query_counts, dag_count, task_count, start_ago, schedule_interval, shape",
        [
            
            ([10, 10, 10, 10], 1, 1, "1d", "None", "no_structure"),
            ([10, 10, 10, 10], 1, 1, "1d", "None", "linear"),