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
execution_date = DEFAULT_DATE
        dag_id = "dag_id"
        task_id = "task_id"
        try_number = 42
        executor = MagicMock()
        scheduler = SchedulerJob(executor=executor)
        scheduler.processor_agent = MagicMock()
        event_buffer = {TaskInstanceKey(dag_id, task_id, execution_date, try_number): (State.SUCCESS, None)}
        executor.get_event_buffer.return_value = event_buffer
        dag = DAG(dag_id=dag_id, start_date=DEFAULT_DATE)
        task = DummyOperator(dag=dag, task_id=task_id)
        with create_session() as session:
            ti = TaskInstance(task, DEFAULT_DATE)
            ti.state = State.SUCCESS
            session.merge(ti)
        scheduler._process_executor_events()
        
        
        assert event_buffer == {}
    def test_execute_task_instances_is_paused_wont_execute(self):