Context:
People have been asking for IPv6 Support on GitHub since years (probably a decade by now)
... and someone even got so annoyed that they decided to setup a dedicated website for checking this: https://isgithubipv6.live/
Honestly this isn't even true anymore. Most major ISPs have implemented dual stack now. The customer doesn't know or care because it's done at the CPE for them.
I use a browser extension which tells me if the site I'm at is 6 or 4 or mixed. In 2024 most major sites support V6. A lot of this is due to CDN supporting it natively.
The fact that GitHub doesn't is quickly becoming the exception.