This tests fails occasionally on mysql at least:

https://github.com/apache/airflow/pull/11555/checks?check_run_id=1260840314#step:9:1125

```
=================================== FAILURES ===================================
_____________ TestSchedulerJob.test_no_orphan_process_will_be_left _____________

self = <tests.jobs.test_scheduler_job.TestSchedulerJob testMethod=test_no_orphan_process_will_be_left>

    def test_no_orphan_process_will_be_left(self):
        empty_dir = mkdtemp()
        current_process = psutil.Process()
        old_children = current_process.children(recursive=True)
        scheduler = SchedulerJob(subdir=empty_dir,
                                 num_runs=1,
                                 executor=MockExecutor(do_update=False))
        scheduler.run()
        shutil.rmtree(empty_dir)
    
        # Remove potential noise created by previous tests.
        current_children = set(current_process.children(recursive=True)) - set(
            old_children)
>       self.assertFalse(current_children)
E       AssertionError: {psutil.Process(pid=3474, name='/usr/local/bin/', status='running', started='19:26:22')} is not false

tests/jobs/test_scheduler_job.py:871: AssertionError
```



tests/jobs/test_scheduler_job.py
task3 = BashOperator(task_id='dummy3', bash_command='true')
        session = settings.Session()
        dagbag = DagBag(
            dag_folder=os.path.join(settings.DAGS_FOLDER, "no_dags.py"),
            include_examples=False,
            read_dags_from_db=True,
        )
        dagbag.bag_dag(dag=dag, root_dag=dag)
        dagbag.sync_to_db(session=session)
        dag_run = dag.create_dagrun(
            run_type=DagRunType.SCHEDULED,
            execution_date=DEFAULT_DATE,
            state=State.RUNNING,
            session=session,
        )
        dag.sync_to_db(session=session)  
        job = SchedulerJob(subdir=os.devnull)
        job.executor = MockExecutor(do_update=False)
        job.processor_agent = mock.MagicMock(spec=DagFileProcessorAgent)
        num_queued = job._do_scheduling(session)
        
        
        session.add(dag_run)
        session.refresh(dag_run)
        assert num_queued == 2
        assert dag_run.state == State.RUNNING
        ti1 = dag_run.get_task_instance(task1.task_id, session)
        assert ti1.state == State.QUEUED
        
        ti1.state = State.SUCCESS