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/workerqueue.go

@@ -42,7 +42,10 @@ type WorkerPoolQueue[T any] struct {
 	workerNumMu     sync.Mutex
 }
 
-type flushType chan struct{}
+type flushType struct {
+	timeout time.Duration
+	c       chan struct{}
+}
 
 var _ ManagedWorkerPoolQueue = (*WorkerPoolQueue[any])(nil)
 
@@ -104,12 +107,12 @@ func (q *WorkerPoolQueue[T]) FlushWithContext(ctx context.Context, timeout time.
 	if timeout > 0 {
 		after = time.After(timeout)
 	}
-	c := make(flushType)
+	flush := flushType{timeout: timeout, c: make(chan struct{})}
 
 	// send flush request
 	// if it blocks, it means that there is a flush in progress or the queue hasn't been started yet
 	select {
-	case q.flushChan <- c:
+	case q.flushChan <- flush:
 	case <-ctx.Done():
 		return ctx.Err()
 	case <-q.ctxRun.Done():
@@ -120,7 +123,7 @@ func (q *WorkerPoolQueue[T]) FlushWithContext(ctx context.Context, timeout time.
 
 	// wait for flush to finish
 	select {
-	case <-c:
+	case <-flush.c:
 		return nil
 	case <-ctx.Done():
 		return ctx.Err()