fix: flaky TestDiscardCardsStage - replace AddWaitStep with AddUntilStep (ppy 139a777)

Agent-Logs-Url: https://github.com/winnerspiros/osu/sessions/4358266f-6e70-4ab4-b19a-b077a433cd27

Co-authored-by: winnerspiros <1675249+winnerspiros@users.noreply.github.com>

Author: Copilot

osu.Game.Tests/Visual/RankedPlay/TestSceneRankedPlayScreen.cs

@@ -60,7 +60,7 @@ public void TestDiscardCardsStage()
 
             AddStep("set discard phase", () => MultiplayerClient.RankedPlayChangeStage(RankedPlayStage.CardDiscard).WaitSafely());
 
-            AddWaitStep("wait", 3);
+            AddUntilStep("wait until cards are present", () => this.ChildrenOfType<PlayerHandOfCards.PlayerHandCard>().Count() == 5);
 
             for (int i = 0; i < 3; i++)
             {