We have flaky scheduler test:


https://github.com/apache/airflow/pull/11659/checks?check_run_id=1279791496#step:6:527


_______________ 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
"""
        Test to check that a DAG returns its active runs
        """
        now = timezone.utcnow()
        six_hours_ago_to_the_hour = (now - datetime.timedelta(hours=6)).replace(
            minute=0, second=0, microsecond=0
        )
        start_date = six_hours_ago_to_the_hour
        dag_name1 = 'get_active_runs_test'
        default_args = {'owner': 'airflow', 'depends_on_past': False, 'start_date': start_date}
        dag1 = DAG(dag_name1, schedule_interval='* * * * *', max_active_runs=1, default_args=default_args)
        run_this_1 = DummyOperator(task_id='run_this_1', dag=dag1)
        run_this_2 = DummyOperator(task_id='run_this_2', dag=dag1)
        run_this_2.set_upstream(run_this_1)
        run_this_3 = DummyOperator(task_id='run_this_3', dag=dag1)
        run_this_3.set_upstream(run_this_2)
        session = settings.Session()
        orm_dag = DagModel(dag_id=dag1.dag_id)
        session.merge(orm_dag)
        session.commit()
        session.close()
        dag1.clear()
        dr = dag1.create_dagrun(
            run_type=DagRunType.SCHEDULED,
            execution_date=start_date,