Images from the wordpress.org pattern directory are not placed in the assets folder on export.

To reproduce:

Activate Twenty Twenty-Three
In any template in the site editor, add a pattern from the pattern directory that has an image,
For example Banners > Opening hours or Forest.
Save the template.

Try to export the theme using the plugin icon in the Site Editor.
I got an error message saying "An error occurred while attempting to export the theme" and the browser console shows
Internal Server Error 500.

Go to the Admin > Appearance > Create block theme, and select export.

Check the content of the zip file.
The pattern was created with a local link, but the image is not in the folder.
<!-- wp:cover {"url":"<?php echo esc_url( get_stylesheet_directory_uri() ); ?>/assets/images/forest.jpg","dimRatio":60,"minHeight":800,"align":"full"} -->