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
)
            date = dag.following_schedule(date)
            ti1 = TaskInstance(task1, dr.execution_date)
            ti2 = TaskInstance(task2, dr.execution_date)
            tis.append(ti1)
            tis.append(ti2)
            ti1.refresh_from_db()
            ti2.refresh_from_db()
            ti1.state = State.SCHEDULED
            ti2.state = State.SCHEDULED
            session.merge(ti1)
            session.merge(ti2)
            session.flush()
        scheduler.max_tis_per_query = 2
        res = scheduler._critical_section_execute_task_instances(session)
        assert 2 == res
        scheduler.max_tis_per_query = 8
        with mock.patch.object(
            type(scheduler.executor), 'slots_available', new_callable=mock.PropertyMock
        ) as mock_slots:
            mock_slots.return_value = 2
            
            assert 2 == res
            res = scheduler._critical_section_execute_task_instances(session)
        res = scheduler._critical_section_execute_task_instances(session)
        assert 4 == res
        for ti in tis:
            ti.refresh_from_db()
            assert State.QUEUED == ti.state
    def test_execute_task_instances_unlimited(self):