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
self, expected_query_counts, dag_count, task_count, start_ago, schedule_interval, shape
    ):
        with mock.patch.dict(
            "os.environ",
            {
                "PERF_DAGS_COUNT": str(dag_count),
                "PERF_TASKS_COUNT": str(task_count),
                "PERF_START_AGO": start_ago,
                "PERF_SCHEDULE_INTERVAL": schedule_interval,
                "PERF_SHAPE": shape,
            },
        ), conf_vars(
            {
                ('scheduler', 'use_job_schedule'): 'True',
                ('core', 'store_serialized_dags'): 'True',
            }
        ):
            dagbag = DagBag(dag_folder=ELASTIC_DAG_FILE, include_examples=False)
            dagbag.sync_to_db()
            mock_agent = mock.MagicMock()
            job = SchedulerJob(subdir=PERF_DAGS_FOLDER, num_runs=1)
            job.executor = MockExecutor(do_update=False)
            job.heartbeat = mock.MagicMock()
            job.processor_agent = mock_agent
            for expected_query_count in expected_query_counts:
                with create_session() as session:
                    with assert_queries_count(expected_query_count):
                        job._do_scheduling(session)