Fix missing disposal

osu.Game/Screens/Edit/EditorBeatmapSkin.cs

@@ -141,6 +141,7 @@ namespace osu.Game.Screens.Edit
         {
             if (Skin.BeatmapSetResources != null)
                 Skin.BeatmapSetResources.CacheInvalidated -= InvokeSkinChanged;
+            Skin.Dispose();
         }
 
         #region Delegated ISkin implementation

osu.Game/Skinning/Skin.cs

@@ -342,6 +342,7 @@ namespace osu.Game.Skinning
 
             Textures?.Dispose();
             Samples?.Dispose();
+            FallbackStore?.Dispose();
 
             store.Dispose();
         }