login to cobranded gitlab site with account moderation has bad error message
Reproduce the bug here:
- go to code.videolan.org
- try to signin with gitlab or github login buttons using an account which does not already have a code.videolan.org account
- WITNESS you receive an error message like this:

Specifically this part matters:
Signing in using your Gitlab.com account without a pre-existing GitLab account is not allowed. Create a GitLab account first, and then connect it to your GitLab.com account.
- WITNESS: this error message makes absolutely no sense and is self-referential.
The error message should say:
Signing in with your gitlab account is not supported without an existing ((code.videolan.org)) account. Create a ((code.videolan.org)) account first, then connect it to your gitlab account.
Where ((code.videolan.org)) is replaced by the cobrand site name
Edited by David Jeske
