This little thingy patch: https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Popups/+/486294 reveals that CS for some reason doesn't catch trailing characters after the types for a PHPDoc @return annotation.
Cases like;
@return array/
should be caught by phpcs and make Jenkins to fail explicitly. @thiemowmde suggest we also tag this as good first task :)