Fix flaky tests due to async disposal

[smoogipoo]

See: https://github.com/ppy/osu/actions/runs/15921735738/job/44909862713?pr=33904

I ran a large subset of tests and found one other case where this could come up (relax mod tests). These are cases where hitobjects/beatmaps are reused between tests, which thankfully isn't common to do.

Repro:

diff --git a/osu.Game/Screens/Play/Player.cs b/osu.Game/Screens/Play/Player.cs
index 6ee3ed13a0..778709ca95 100644
--- a/osu.Game/Screens/Play/Player.cs
+++ b/osu.Game/Screens/Play/Player.cs
@@ -1164,6 +1164,12 @@ public override void OnSuspending(ScreenTransitionEvent e)
             base.OnSuspending(e);
         }
 
+        protected override void Dispose(bool isDisposing)
+        {
+            Thread.Sleep(1000);
+            base.Dispose(isDisposing);
+        }
+
         public override bool OnExiting(ScreenExitEvent e)
         {
             screenSuspension?.RemoveAndDisposeImmediately();