Login on https://gitlab.gnome.org fails when using the GitLab account (OAuth) option

Summary

"Could not authenticate you from GitLab because "Api v3 is no longer supported. use api v4 instead.: {"error":"api v3 is no longer supported. use api v4 instead."}"

Steps to reproduce

Visit https://gitlab.gnome.org/users/sign_in

1. Fill out user account details
2. Choose "Sign in with GitLab"

We're running GitLab version 10.8.4 (2268d0cf).

Nothing in particular changed on our side, these failures have started occurring around Friday 08th of June.

Multiple contributors are locked out from their accounts due to this.

Thanks,