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 that the dag file processor does not call the sla_miss_callback when a
        notification has already been sent
        """
        session = settings.Session()
        
        sla_callback = MagicMock()
        
        
        test_start_date = days_ago(2)
        dag = DAG(
            dag_id='test_sla_miss',
            sla_miss_callback=sla_callback,
            default_args={'start_date': test_start_date, 'sla': datetime.timedelta(days=1)},
        )
        task = DummyOperator(task_id='dummy', dag=dag, owner='airflow')
        
        session.merge(TaskInstance(task=task, execution_date=test_start_date, state='success'))
        
        session.merge(
            SlaMiss(
                task_id='dummy',
                dag_id='test_sla_miss',
                execution_date=test_start_date,
                email_sent=False,
                notification_sent=True,
            )
        )