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/models/test_taskinstance.py
"""
        test that try to create a task with pool_slots less than 1
        """
        def create_task_instance():
            dag = models.DAG(dag_id='test_run_pooling_task')
            task = DummyOperator(
                task_id='test_run_pooling_task_op',
                dag=dag,
                pool='test_pool',
                pool_slots=0,
                owner='airflow',
                start_date=timezone.datetime(2016, 2, 1, 0, 0, 0),
            )
            return TI(task=task, execution_date=timezone.utcnow())
        with pytest.raises(AirflowException):
            create_task_instance()
    @provide_session
    def test_ti_updates_with_task(self, session=None):
        """
        test that updating the executor_config propagates to the TaskInstance DB
        """
        with models.DAG(dag_id='test_run_pooling_task') as dag:
            task = DummyOperator(
                task_id='test_run_pooling_task_op',
                owner='airflow',
                executor_config={'foo': 'bar'},
                start_date=timezone.datetime(2016, 2, 1, 0, 0, 0),