tests/pass/concurrency/sync: try to make it less likely for the test …

…to fail on macOS

tests/pass/concurrency/sync.rs

@@ -79,7 +79,7 @@ fn check_conditional_variables_timed_wait_notimeout() {
     let guard = lock.lock().unwrap();
 
     let handle = thread::spawn(move || {
-        thread::sleep(Duration::from_millis(100)); // Make sure the other thread is waiting by the time we call `notify`.
+        thread::sleep(Duration::from_millis(10)); // Make sure the other thread is waiting by the time we call `notify`.
         let (_lock, cvar) = &*pair2;
         cvar.notify_one();
     });