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
naive_datetime = DEFAULT_DATE.replace(tzinfo=None)
        
        op_no_dag = DummyOperator(task_id='op_no_dag')
        ti = TI(task=op_no_dag, execution_date=naive_datetime)
        assert ti.execution_date == DEFAULT_DATE
        
        dag = DAG('dag', start_date=DEFAULT_DATE)
        op1 = DummyOperator(task_id='op_1')
        dag.add_task(op1)
        ti = TI(task=op1, execution_date=naive_datetime)
        assert ti.execution_date == DEFAULT_DATE
        
        tzinfo = pendulum.timezone("Europe/Amsterdam")
        execution_date = timezone.datetime(2016, 1, 1, 1, 0, 0, tzinfo=tzinfo)
        utc_date = timezone.convert_to_utc(execution_date)
        ti = TI(task=op1, execution_date=execution_date)
        assert ti.execution_date == utc_date
    def test_task_naive_datetime(self):