time: reduce iteration count in short_sleeps test (#6052)

tokio/tests/time_sleep.rs

@@ -189,7 +189,7 @@ async fn greater_than_max() {
 
 #[tokio::test]
 async fn short_sleeps() {
-    for _ in 0..10000 {
+    for _ in 0..1000 {
         tokio::time::sleep(std::time::Duration::from_millis(0)).await;
     }
 }