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
include_examples=False,
            read_dags_from_db=False,
        )
        dagbag.bag_dag(dag=dag, root_dag=dag)
        
        DAG.bulk_write_to_db(dagbag.dags.values())
        dag_model = DagModel.get_dagmodel(dag.dag_id)
        
        assert dag_model.next_dagrun == DEFAULT_DATE
        dag = SerializedDAG.from_dict(SerializedDAG.to_dict(dag))
        dagrun = dag.create_dagrun(
            run_type=DagRunType.SCHEDULED,
            execution_date=dag_model.next_dagrun,
            start_date=timezone.utcnow(),
            state=State.RUNNING,
            external_trigger=False,
            session=session,
            creating_job_id=2,
        )
        session.flush()
        assert dag.get_last_dagrun(session) == dagrun
        scheduler = SchedulerJob(subdir=os.devnull, executor=self.null_exec)
        scheduler.dagbag = dagbag
        scheduler.processor_agent = mock.MagicMock()
        
        scheduler._create_dag_runs([dag_model], session)
        
        assert dag_model.next_dagrun == DEFAULT_DATE + timedelta(days=1)
        session.rollback()
    def test_do_schedule_max_active_runs_upstream_failed(self):