A regular anchor tag would work in all situations on all browsers. Unfortunately github doesn't care about that.
P.S. jlelse, you should actually allow http rather than doing a 301 redirect.
curl https://jlelse.blog/backend/webmention -d "source=http://superkuh.com/hosting-on-github-is-its-own-problem.html" -d "target=https://jlelse.blog/links/2020/02/rss-bridge/"
[comment on this post] Append "/@say/your message here" to the URL in the location bar and hit enter.