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)
        with dag:
            op1 = DummyOperator(task_id='test_op_1', owner='test')
            op2 = DummyOperator(task_id='test_op_2', owner='test')
            op3 = DummyOperator(task_id='test_op_3', owner='test')
            op1 >> op2 << op3
        
        assert op2 in op1.downstream_list
        assert op2 in op3.downstream_list
    @patch.object(DAG, 'get_concurrency_reached')
    def test_requeue_over_dag_concurrency(self, mock_concurrency_reached):
        mock_concurrency_reached.return_value = True
        dag = DAG(
            dag_id='test_requeue_over_dag_concurrency',
            start_date=DEFAULT_DATE,
            max_active_runs=1,
            concurrency=2,
        )
        task = DummyOperator(task_id='test_requeue_over_dag_concurrency_op', dag=dag)
        ti = TI(task=task, execution_date=timezone.utcnow(), state=State.QUEUED)
        
        with create_session() as session:
            session.add(ti)
            session.commit()
        ti.run()
        assert ti.state == State.NONE
    def test_requeue_over_task_concurrency(self):