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
self.callback_ran = True
        session = settings.Session()
        temp_instance = (
            session.query(TI)
            .filter(TI.task_id == self.task_id)
            .filter(TI.dag_id == self.dag_id)
            .filter(TI.execution_date == self.execution_date)
            .one()
        )
        self.task_state_in_callback = temp_instance.state
class TestTaskInstance(unittest.TestCase):
    @staticmethod
    def clean_db():
        db.clear_db_dags()
        db.clear_db_pools()
        db.clear_db_runs()
        db.clear_db_task_fail()
        db.clear_rendered_ti_fields()
        db.clear_db_task_reschedule()
    def setUp(self):
        self.clean_db()
        with create_session() as session:
            test_pool = Pool(pool='test_pool', slots=1)
            session.add(test_pool)
            session.commit()
    def tearDown(self):
        self.clean_db()
    def test_set_task_dates(self):