Even though currently github pages does not support IPv6, their CDN fastly does.
Please do this only If you know what you are doing! This IP can change at any moment.
To add IPv6 support, add a AAAA reccord in your DNS with the following IPv6 address.
This IP is the anycasted IPv6 address of Fasly CDN which serves Github Pages. It is recommended to use this with Cloudflare Proxy as HTTPS does not work with custom domains with this IP.
In fact this blog is powered with IPv6 Github Pages.