This probably means you’re running an older version of WordPress or an SEO plugin is automatically blocking this folder in the robots.txt file.
To fix the issue update WordPress to the latest version and make sure any plugins are not changing the robots.txt file.
From version 4 of WordPress the wp-include folder is not blocked so you should be good to go.
It’s OK to allow Google to crawl wp-includes so it can look at the plugin files and try to figure out what the different features of your website do. Helping Google understand more about your pages is really important.