I see this in logs on server shutdown:

```
2022.01.30 02:51:22.856463 [ 755777 ] {} <Error> void DB::MergeTreeBackgroundExecutor<DB::MergeMutateRuntimeQueue>::routine(DB::TaskRuntimeDataPtr) [Queue = DB::MergeMutateRuntimeQueue]: Code: 236. DB::Exception: Cancelled merging parts.
```

but it's not an error.

Log level should be changed and it should not show stack trace.
{
    {
        std::lock_guard lock(mutex);
        shutdown = true;
        has_tasks.notify_all();
    }
    pool.wait();
}
template <class Queue>
bool MergeTreeBackgroundExecutor<Queue>::trySchedule(ExecutableTaskPtr task)
{
    std::lock_guard lock(mutex);
    if (shutdown)
        return false;
    auto & value = CurrentMetrics::values[metric];
    if (value.load() >= static_cast<int64_t>(max_tasks_count))
        return false;
    pending.push(std::make_shared<TaskRuntimeData>(std::move(task), metric));
    has_tasks.notify_one();
    return true;
}
template <class Queue>
void MergeTreeBackgroundExecutor<Queue>::removeTasksCorrespondingToStorage(StorageID id)