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 = models.DAG(dag_id='test_check_and_change_state_before_execution')
        task = DummyOperator(task_id='task', dag=dag, start_date=DEFAULT_DATE)
        ti = TI(task=task, execution_date=timezone.utcnow())
        assert ti._try_number == 0
        assert ti.check_and_change_state_before_execution()
        
        assert ti.state == State.RUNNING
        assert ti._try_number == 1
    def test_check_and_change_state_before_execution_dep_not_met(self):
        dag = models.DAG(dag_id='test_check_and_change_state_before_execution')
        task = DummyOperator(task_id='task', dag=dag, start_date=DEFAULT_DATE)
        task2 = DummyOperator(task_id='task2', dag=dag, start_date=DEFAULT_DATE)
        task >> task2
        ti = TI(task=task2, execution_date=timezone.utcnow())
        assert not ti.check_and_change_state_before_execution()
    def test_try_number(self):
        """
        Test the try_number accessor behaves in various running states
        """
        dag = models.DAG(dag_id='test_check_and_change_state_before_execution')
        task = DummyOperator(task_id='task', dag=dag, start_date=DEFAULT_DATE)
        ti = TI(task=task, execution_date=timezone.utcnow())
        assert 1 == ti.try_number
        ti.try_number = 2
        ti.state = State.RUNNING
        assert 2 == ti.try_number
        ti.state = State.SUCCESS
        assert 3 == ti.try_number
    def test_get_num_running_task_instances(self):