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
"""
        Test if no on_*_callback are defined on DAG, Callbacks not registered and sent to DAG Processor
        """
        dag = DAG(
            dag_id='test_dagrun_callbacks_are_not_added_when_callbacks_are_not_defined',
            start_date=DEFAULT_DATE,
        )
        BashOperator(task_id='test_task', dag=dag, owner='airflow', bash_command='echo hi')
        scheduler = SchedulerJob(subdir=os.devnull)
        scheduler.processor_agent = mock.Mock()
        scheduler.processor_agent.send_callback_to_execute = mock.Mock()
        scheduler._send_dag_callbacks_to_processor = mock.Mock()
        
        with mock.patch.object(settings, "STORE_DAG_CODE", False):
            scheduler.dagbag.bag_dag(dag, root_dag=dag)
            scheduler.dagbag.sync_to_db()
        session = settings.Session()
        orm_dag = session.query(DagModel).get(dag.dag_id)
        assert orm_dag is not None
        
        scheduler._create_dag_runs([orm_dag], session)
        drs = DagRun.find(dag_id=dag.dag_id, session=session)
        assert len(drs) == 1
        dr = drs[0]