Why would you ever want to share a valid Github API key publicly?
It probably wasn't the best idea, but it was the only "secret" needed in the whole project and I didn't want to maintain a way of managing secrets in a public project for a pointless key.
In the end I did just that, and looking back it was the better choice, but at the time it was annoying.
I wonder why they'd want to invalidate that. :)