Comments: Add rel="nofollow ugc" attribute to links in comments.
rel="nofollow ugc"
UGC stands for User Generated Content, and the ugc attribute value is recommended for links within user generated content, such as comments and forum posts.
ugc
See https://webmasters.googleblog.com/2019/09/evolving-nofollow-new-ways-to-identify.html.
Props audrasjb, joostdevalk, dkarfa, SergeyBiryukov. Fixes #48022.