Add optional skin foreign key to databased settings

osu.Game/Skinning/SkinStore.cs

@@ -1,6 +1,8 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
+using System.Linq;
+using Microsoft.EntityFrameworkCore;
 using osu.Framework.Platform;
 using osu.Game.Database;
 
@@ -12,5 +14,9 @@ namespace osu.Game.Skinning
             : base(contextFactory, storage)
         {
         }
+
+        protected override IQueryable<SkinInfo> AddIncludesForDeletion(IQueryable<SkinInfo> query) =>
+            base.AddIncludesForDeletion(query)
+                .Include(s => s.Settings); // don't include FileInfo. these are handled by the FileStore itself.
     }
 }