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/jobs/test_scheduler_job.py
dag = SerializedDAG.from_dict(SerializedDAG.to_dict(dag))
        scheduler = SchedulerJob(executor=self.null_exec)
        scheduler.processor_agent = mock.MagicMock()
        
        dr = dag.create_dagrun(
            run_type=DagRunType.SCHEDULED,
            execution_date=DEFAULT_DATE,
            state=State.RUNNING,
        )
        scheduler._schedule_dag_run(dr, {}, session)
        dr = dag.create_dagrun(
            run_type=DagRunType.SCHEDULED,
            execution_date=dag.following_schedule(dr.execution_date),
            state=State.RUNNING,
        )
        scheduler._schedule_dag_run(dr, {}, session)
        task_instances_list = scheduler._executable_task_instances_to_queued(max_tis=32, session=session)
        assert len(task_instances_list) == 1
    def test_scheduler_verify_pool_full_2_slots_per_task(self):
        """
        Test task instances not queued when pool is full.
        Variation with non-default pool_slots
        """
        dag = DAG(dag_id='test_scheduler_verify_pool_full_2_slots_per_task', start_date=DEFAULT_DATE)
        BashOperator(
            task_id='dummy',
            dag=dag,
            owner='airflow',
            pool='test_scheduler_verify_pool_full_2_slots_per_task',
            pool_slots=2,