The issue is resolved now, the repo is available again.
We have not received any response to the support case that we opened, but we assume that it was a false positive of some automatic algorithm.
As a consequence of this we're going to set up a mirror outside Github so that the work didn't stop if something like that happens again.
UPD: We received the official response explaining that this was a mistake. I must admit the whole situation was resolved really quickly, good job.