WikidataPageBanner is run in production so this blocks the deprecation of SkinTemplateOutputPageBeforeExec
WikidataPageBanner sets prebodyhtml and manipulates the subtitle keys.
WikidataPageBanner per https://www.mediawiki.org/wiki/User:Jdlrobson/Skins_for_extension_developers#Modifying_subtitle should use the OutputPage methods clearSubtitle, getSubtitle, and addSubtitle to get the same effect instead of using the template key prebodyhtml which will soon not mean anything.