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,
        state,
        start_date,
        end_date,
    ):
        """
        Test if _process_task_instances puts the right task instances into the
        mock_list.
        """
        dag = DAG(dag_id='test_scheduler_process_execute_task_with_task_concurrency', start_date=DEFAULT_DATE)
        BashOperator(task_id='dummy', task_concurrency=2, dag=dag, owner='airflow', bash_command='echo Hi')
        with create_session() as session:
            orm_dag = DagModel(dag_id=dag.dag_id)
            session.merge(orm_dag)
        dag = SerializedDAG.from_dict(SerializedDAG.to_dict(dag))
        scheduler = SchedulerJob(subdir=os.devnull)
        scheduler.processor_agent = mock.MagicMock()
        scheduler.dagbag.bag_dag(dag, root_dag=dag)
        dag.clear()
        dr = dag.create_dagrun(
            run_type=DagRunType.SCHEDULED,
            execution_date=DEFAULT_DATE,
            state=State.RUNNING,
        )
        assert dr is not None
        with create_session() as session:
            ti = dr.get_task_instances(session=session)[0]
            ti.state = state
            ti.start_date = start_date
            ti.end_date = end_date