Make the throttler tests more stable (#5941)
Make the throttler tests more stable (#5941)

* Make the throttler tests more stable

Remove sleeps and make sure the inner function might also fail,
since this is what will happen in reality if the context times out.
Add a test that will go through both paths.

```
gt -race -count=10
PASS
```

* move sorting to the helper

* also fix todo

knative/serving,knative/serving