sleep while waiting for pwm export

Co-authored-by: J M <2364004+Blu-J@users.noreply.github.com>

backend/src/sound.rs

@@ -40,7 +40,9 @@ impl SoundInterface {
         let instant = Instant::now();
         while tokio::fs::metadata(&*PERIOD_FILE).await.is_err()
             && instant.elapsed() < Duration::from_secs(1)
-        {}
+        {
+            tokio::time::sleep(Duration::from_millis(1));
+        }
         Ok(SoundInterface(Some(guard)))
     }
     #[instrument(skip(self))]