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_pendulum_template_dates',
            schedule_interval='0 12 * * *',
            start_date=timezone.datetime(2016, 6, 1, 0, 0, 0),
        )
        task = DummyOperator(task_id='test_pendulum_template_dates_task', dag=dag)
        ti = TI(task=task, execution_date=timezone.utcnow())
        template_context = ti.get_template_context()
        assert isinstance(template_context["execution_date"], pendulum.DateTime)
        assert isinstance(template_context["next_execution_date"], pendulum.DateTime)
        assert isinstance(template_context["prev_execution_date"], pendulum.DateTime)
    @parameterized.expand(
        [
            ('{{ var.value.a_variable }}', 'a test value'),
            ('{{ var.value.get("a_variable") }}', 'a test value'),
            ('{{ var.value.get("a_variable", "unused_fallback") }}', 'a test value'),
            ('{{ var.value.get("missing_variable", "fallback") }}', 'fallback'),
        ]
    )
    def test_template_with_variable(self, content, expected_output):