The test fails quite regularly - usually in one of many jobs:

Example


https://github.com/apache/airflow/pull/12850/checks?check_run_id=1506517544

```
______________ TestSchedulerJob.test_scheduler_task_start_date ________________

self = <tests.jobs.test_scheduler_job.TestSchedulerJob testMethod=test_scheduler_task_start_date>

    def test_scheduler_task_start_date(self):
        """
        Test that the scheduler respects task start dates that are different from DAG start dates
        """
    
        dagbag = DagBag(dag_folder=os.path.join(settings.DAGS_FOLDER, "no_dags.py"), include_examples=False)
        dag_id = 'test_task_start_date_scheduling'
        dag = self.dagbag.get_dag(dag_id)
        dag.is_paused_upon_creation = False
        dagbag.bag_dag(dag=dag, root_dag=dag)
    
        # Deactivate other dags in this file so the scheduler doesn't waste time processing them
        other_dag = self.dagbag.get_dag('test_start_date_scheduling')
        other_dag.is_paused_upon_creation = True
        dagbag.bag_dag(dag=other_dag, root_dag=other_dag)
    
        dagbag.sync_to_db()
    
        scheduler = SchedulerJob(executor=self.null_exec, subdir=dag.fileloc, num_runs=2)
        scheduler.run()
    
        session = settings.Session()
        tiq = session.query(TaskInstance).filter(TaskInstance.dag_id == dag_id)
        ti1s = tiq.filter(TaskInstance.task_id == 'dummy1').all()
        ti2s = tiq.filter(TaskInstance.task_id == 'dummy2').all()
        self.assertEqual(len(ti1s), 0)
>       self.assertEqual(len(ti2s), 2)
E       AssertionError: 1 != 2

tests/jobs/test_scheduler_job.py:2415: AssertionError


```

tests/cli/commands/test_jobs_command.py
with create_session() as session:
            for _ in range(3):
                job = SchedulerJob()
                job.state = State.RUNNING
                session.add(job)
            session.commit()
            job.heartbeat()
        with contextlib.redirect_stdout(io.StringIO()) as temp_stdout:
            jobs_command.check(
                self.parser.parse_args(
                    ['jobs', 'check', '--job-type', 'SchedulerJob', '--limit', '100', '--allow-multiple']
                )
            )
        self.assertIn("Found 3 alive jobs.", temp_stdout.getvalue())
    def test_should_ignore_not_running_jobs(self):
        with create_session() as session:
            for _ in range(3):
                job = SchedulerJob()
                job.state = State.SHUTDOWN
                session.add(job)
            session.commit()
        
        with pytest.raises(SystemExit, match=r"No alive jobs found."):
            jobs_command.check(self.parser.parse_args(['jobs', 'check']))
    def test_should_raise_exception_for_multiple_scheduler_on_one_host(self):