I don’t use WP but I would not want anything served from an include folder, With the coding I do I never allow access to this type of folder period … And as the directory name suggests there files are included in other files
This error is telling you that someone (maybe a crawler from your hosting provider) tried to access that folder by it’s url and the web server could not find a valid index file to show. Just put an empty index.php in that folder, that will get you rid from that message and prevent any unwanted visitors to list the contents in case you have directory listing enabled. In fact, consider it a good practice putting empty index files in all your sensitive folders, specially with WP