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
dag = DAG('dag', start_date=DEFAULT_DATE)
        op1 = DummyOperator(task_id='op_1', owner='test', dag=dag)
        ti = TI(task=op1, execution_date=timezone.utcnow(), state=State.RUNNING)
        start_date = timezone.utcnow()
        ti.start_date = start_date
        ti.set_state(State.UP_FOR_RETRY)
        assert ti.state == State.UP_FOR_RETRY
        assert ti.start_date == start_date, "Start date should have been left alone"
        assert ti.start_date < ti.end_date
        assert ti.duration > 0
@pytest.mark.parametrize("pool_override", [None, "test_pool2"])
def test_refresh_from_task(pool_override):