fix implicit casting in As.Expression

Author: olmobrutall

Signum.Test/Environment/Entities.cs

@@ -80,7 +80,7 @@ public class ArtistEntity : Entity, IAuthorEntity
         public AwardEntity? LastAward { get; set; }
 
         [AutoExpressionField]
-        public IEnumerable<Lite<Entity>> FriendsCovariant() => As.Expression(() => Friends);
+        public IEnumerable<Lite<Entity>> FriendsCovariant() => As.Expression(() => (IEnumerable<Lite<Entity>>)Friends);
 
         public MList<Lite<ArtistEntity>> Friends { get; set; } = new MList<Lite<ArtistEntity>>();