Spotted on production:
Warning: OutputPage::getModuleStyles: style module should define its position explicitly: ext.geshi.language.bash ResourceLoaderGeSHiModule [Called from OutputPage::getModuleStyles in /srv/mediawiki/php-1.26wmf8/includes/OutputPage.php at line 603] in /srv/mediawiki/php-1.26wmf8/includes/debug/MWDebug.php on line 300