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/testlogger/testlogger.go

@@ -118,7 +118,7 @@ func PrintCurrentTest(t testing.TB, skip ...int) func() {
 				_, _ = fmt.Fprintf(os.Stdout, "+++ %s ... still flushing after %v ...\n", t.Name(), SlowFlush)
 			}
 		})
-		if err := queue.GetManager().FlushAll(context.Background(), time.Minute); err != nil {
+		if err := queue.GetManager().FlushAll(context.Background(), -1); err != nil {
 			t.Errorf("Flushing queues failed with error %v", err)
 		}
 		timer.Stop()