Reduce integration test overhead (#32475)

In profiling integration tests, I found a couple places where per-test
overhead could be reduced:

* Avoiding disk IO by synchronizing instead of deleting & copying test
Git repository data. This saves ~100ms per test on my machine
* When flushing queues in `PrintCurrentTest`, invoke `FlushWithContext`
in a parallel.

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/queue/workergroup.go

@@ -197,15 +197,30 @@ func (q *WorkerPoolQueue[T]) doFlush(wg *workerGroup[T], flush flushType) {
 	defer log.Debug("Queue %q finishes flushing", q.GetName())
 
 	// stop all workers, and prepare a new worker context to start new workers
-
 	wg.ctxWorkerCancel()
 	wg.wg.Wait()
 
 	defer func() {
-		close(flush)
+		close(flush.c)
 		wg.doPrepareWorkerContext()
 	}()
 
+	if flush.timeout < 0 {
+		// discard everything
+		wg.batchBuffer = nil
+		for {
+			select {
+			case <-wg.popItemChan:
+			case <-wg.popItemErr:
+			case <-q.batchChan:
+			case <-q.ctxRun.Done():
+				return
+			default:
+				return
+			}
+		}
+	}
+
 	// drain the batch channel first
 loop:
 	for {