fix: add only new asset folders to the package (#2674)

Closes #2667

Author: laske185

sources/assets/Stride.Core.Assets/Package.cs

@@ -1109,7 +1109,7 @@ internal void UpdateSourceFolders(IReadOnlyCollection<AssetItem> assets)
                 }
 
                 var assetFolderAbsolute = UPath.Combine(RootDirectory, asset.SourceFolder);
-                if (!assetFolders.Add(assetFolderAbsolute))
+                if (assetFolders.Add(assetFolderAbsolute))
                 {
                     AssetFolders.Add(new AssetFolder(assetFolderAbsolute));
                     IsDirty = true;