How does github not have an AAAA record in 2020?? The faster people move to gitlab the better. ipv6 servers are not at all rare. Useful for individual use since you can save $1/month by dropping a useless for personal use feature.
Last time I launched a new website it took less than a month for someone to let us know that we'd forgotten to configure a AAAA and our site was inaccessible for them. And that was at new website traffic volume.
So yea, GitHub definitely knows about AAAA records and has intentionally decided not to have one. The question is: why? They must have a reason. Maybe even a good one. I'm curious.
A broken AAAA record, perhaps. Sometimes the AAAA is invalid or broken without getting noticed by the sysadmin. I've personally reported broken AAAA records before.