Try the following:
$ nslookup github.com
[...]
Non-authoritative answer:
Name: github.com
Address: 140.82.121.3
See also the completely ignored post in their forums.
comment from the forum:
New ISPs in my country are IPv6-only because there is no new IPv4 space to be provided to them. They do have a over-shared IPv4 address by CGNAT but due to the oversharing, it is unstable and not rare to be offline. For these companies, the internet access is stable only in IPv6.
Thinking about the server-side, some cloud providers are making extra charges for IPv4 addresses (e.g.: Vultr.com) so most of the servers in my company are IPv6-only. Cloning github repositories is very cumbersome due to the lack of IPv6 support and this issue affects me and my team mates on a daily basis.
The math is simple: there are 4.88 billion internet users in the world but the IPv4 space only provides 4 billion addresses. It’s over: IPv4 is obsolete and is provided in a legacy mode. Current applications and services must be IPv6 enabled otherwise it should be seen as obsolete. For that matter, Github.com is an obsolete service because it relies on obsolete technology as IPv4.
I wonder if they ever contacted github support, and what their answer was - rather than only posting on a public forum github doesn’t feel compelled to answer or make official responses to.