Fix hover propagating through toolbar buttons

Closes #21920.

Weirdly enough this was semeingly fixed once before in ancient times in
3891f467a3, but then unfixed again in
566e09083f. The second change is no longer
needed since the toolbar became opaque in #9447.

osu.Game/Overlays/Toolbar/ToolbarButton.cs

@@ -179,7 +179,7 @@ namespace osu.Game.Overlays.Toolbar
             HoverBackground.FadeIn(200);
             tooltipContainer.FadeIn(100);
 
-            return base.OnHover(e);
+            return true;
         }
 
         protected override void OnHoverLost(HoverLostEvent e)