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
scenario = [State.SUCCESS, State.FAILED, State.SUCCESS]
        ti_list = self._test_previous_dates_setup(schedule_interval, catchup, scenario)
        assert ti_list[0].get_previous_ti() is None
        assert ti_list[2].get_previous_ti().execution_date == ti_list[1].execution_date
        assert ti_list[2].get_previous_ti().execution_date != ti_list[0].execution_date
    @parameterized.expand(_prev_dates_param_list)
    def test_previous_ti_success(self, _, schedule_interval, catchup) -> None:
        scenario = [State.FAILED, State.SUCCESS, State.FAILED, State.SUCCESS]
        ti_list = self._test_previous_dates_setup(schedule_interval, catchup, scenario)
        assert ti_list[0].get_previous_ti(state=State.SUCCESS) is None
        assert ti_list[1].get_previous_ti(state=State.SUCCESS) is None
        assert ti_list[3].get_previous_ti(state=State.SUCCESS).execution_date == ti_list[1].execution_date
        assert ti_list[3].get_previous_ti(state=State.SUCCESS).execution_date != ti_list[2].execution_date
    @parameterized.expand(_prev_dates_param_list)
    def test_previous_execution_date_success(self, _, schedule_interval, catchup) -> None:
        scenario = [State.FAILED, State.SUCCESS, State.FAILED, State.SUCCESS]
        ti_list = self._test_previous_dates_setup(schedule_interval, catchup, scenario)
        assert ti_list[0].get_previous_execution_date(state=State.SUCCESS) is None
        assert ti_list[1].get_previous_execution_date(state=State.SUCCESS) is None
        assert ti_list[3].get_previous_execution_date(state=State.SUCCESS) == ti_list[1].execution_date
        assert ti_list[3].get_previous_execution_date(state=State.SUCCESS) != ti_list[2].execution_date
    @parameterized.expand(_prev_dates_param_list)
    def test_previous_start_date_success(self, _, schedule_interval, catchup) -> None:
        scenario = [State.FAILED, State.SUCCESS, State.FAILED, State.SUCCESS]
        ti_list = self._test_previous_dates_setup(schedule_interval, catchup, scenario)
        assert ti_list[0].get_previous_start_date(state=State.SUCCESS) is None
        assert ti_list[1].get_previous_start_date(state=State.SUCCESS) is None
        assert ti_list[3].get_previous_start_date(state=State.SUCCESS) == ti_list[1].start_date
        assert ti_list[3].get_previous_start_date(state=State.SUCCESS) != ti_list[2].start_date
    def test_get_previous_start_date_none(self):