sync: give finalizers more time in TestPoolGC

If we report a leak, make sure we've waited long enough to be sure.
The new sleep regimen waits 1.05 seconds before failing; the old
one waited 0.005 seconds.

(The single linux/amd64 failure in this test feels more like a
timing problem than a leak. I don't want to spend time on it unless
we're sure.)

LGTM=bradfitz
R=bradfitz
CC=golang-codereviews
https://golang.org/cl/72630043

src/pkg/sync/pool_test.go

@@ -87,7 +87,7 @@ func TestPoolGC(t *testing.T) {
 	}
 	for i := 0; i < 5; i++ {
 		runtime.GC()
-		time.Sleep(time.Millisecond)
+		time.Sleep(time.Duration(i*100+10) * time.Millisecond)
 		// 1 pointer can remain on stack or elsewhere
 		if atomic.LoadUint32(&fin) >= N-1 {
 			return