At least now they have to go through that effort again
Does GitLab have this issue? Don't they offer all this for free, unlike GitHub?
I don't know if they handle this case better specifically, but I found almost all GitLab page functionality is better than GitHub - plus it's more generic, you can wire any static page generator into the built-in CI/CD, not just limited to jekyll or doing it yourself.
GitLab requires you to put a txt record with a verification code in your custom private domain DNS to verify ownership.