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.
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.