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
session = settings.Session()
        test_start_date = days_ago(2)
        dag = DAG(
            dag_id='test_sla_miss',
            default_args={'start_date': test_start_date, 'sla': datetime.timedelta(days=1)},
        )
        email1 = 'test1@test.com'
        task = DummyOperator(
            task_id='sla_missed', dag=dag, owner='airflow', email=email1, sla=datetime.timedelta(hours=1)
        )
        session.merge(TaskInstance(task=task, execution_date=test_start_date, state='Success'))
        email2 = 'test2@test.com'
        DummyOperator(task_id='sla_not_missed', dag=dag, owner='airflow', email=email2)
        session.merge(SlaMiss(task_id='sla_missed', dag_id='test_sla_miss', execution_date=test_start_date))
        dag_file_processor = DagFileProcessor(dag_ids=[], log=mock.MagicMock())
        dag_file_processor.manage_slas(dag=dag, session=session)
        assert len(mock_send_email.call_args_list) == 1
        send_email_to = mock_send_email.call_args_list[0][0][0]
        assert email1 in send_email_to
        assert email2 not in send_email_to
    @mock.patch('airflow.jobs.scheduler_job.Stats.incr')
    @mock.patch("airflow.utils.email.send_email")
    def test_dag_file_processor_sla_miss_email_exception(self, mock_send_email, mock_stats_incr):