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
has_task_concurrency_limits=False,
        )
        session.add(dag_model)
        date = dag.start_date
        tis = []
        for _ in range(0, 20):
            dr = dag.create_dagrun(
                run_type=DagRunType.SCHEDULED,
                execution_date=date,
                state=State.RUNNING,
            )
            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 = 0
        scheduler.executor = MagicMock(slots_available=36)
        res = scheduler._critical_section_execute_task_instances(session)
        
        self.assertEqual(36, res)
        session.rollback()
    def test_change_state_for_tis_without_dagrun(self):