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
dag_model = session.query(DagModel).get(dag.dag_id)
        assert dag_model.next_dagrun == DEFAULT_DATE
        job = SchedulerJob(subdir=os.devnull)
        job.executor = MockExecutor(do_update=False)
        job.processor_agent = mock.MagicMock(spec=DagFileProcessorAgent)
        
        
        job._do_scheduling(session)
        dr1 = dag.get_dagrun(DEFAULT_DATE, session)
        assert dr1 is not None
        assert dr1.state == State.RUNNING
        
        dag_model = session.query(DagModel).get(dag.dag_id)
        assert dag_model.next_dagrun == DEFAULT_DATE + timedelta(minutes=1)
        
        dr = dag.create_dagrun(
            state=State.RUNNING,
            execution_date=timezone.utcnow(),
            run_type=DagRunType.MANUAL,
            session=session,
            external_trigger=True,
        )
        assert dr is not None
        
        DAG.bulk_write_to_db([dag], session)
        
        
        dag_model = session.query(DagModel).get(dag.dag_id)
        assert dag_model.next_dagrun == DEFAULT_DATE + timedelta(minutes=1)
    def test_scheduler_create_dag_runs_check_existing_run(self):