Fix queue worker incorrectly stopped when there are still more items in the queue (#29532) #29546

…in the queue (go-gitea#29532) Without `case <-t.C`, the workers would stop incorrectly, the test won't pass. For the worse case, there might be only one running worker processing the queue items for long time because other workers are stopped. The root cause is related to the logic of doDispatchBatchToWorker. It isn't a serious problem at the moment, so keep it as-is.