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 tasks properly take start/end dates from DAGs
        """
        dag = DAG('dag', start_date=DEFAULT_DATE, end_date=DEFAULT_DATE + datetime.timedelta(days=10))
        op1 = DummyOperator(task_id='op_1', owner='test')
        assert op1.start_date is None and op1.end_date is None
        
        dag.add_task(op1)
        assert op1.start_date == dag.start_date and op1.end_date == dag.end_date
        op2 = DummyOperator(
            task_id='op_2',
            owner='test',
            start_date=DEFAULT_DATE - datetime.timedelta(days=1),
            end_date=DEFAULT_DATE + datetime.timedelta(days=11),
        )
        
        dag.add_task(op2)
        assert op2.start_date == dag.start_date and op2.end_date == dag.end_date
        op3 = DummyOperator(
            task_id='op_3',
            owner='test',
            start_date=DEFAULT_DATE + datetime.timedelta(days=1),
            end_date=DEFAULT_DATE + datetime.timedelta(days=9),
        )
        
        dag.add_task(op3)
        assert op3.start_date == DEFAULT_DATE + datetime.timedelta(days=1)
        assert op3.end_date == DEFAULT_DATE + datetime.timedelta(days=9)
    def test_timezone_awareness(self):