Sadly, the CI does not work on forked since it requires the GITHUB_APP private key. See the github action logs here

@mxmehl Do you know if there is a workaround for this?

There certainly would be a workaround but that would mean that all forks can access this secret - which we probably don't want as it's a public project. I think there is an option that such Runs have to be approved by a member, this could be an alternative.

But the easiest solution is if an existing OSRD member just adds the new user instead of them adding themselves. Org members usually have push access to this repo, and thereby also access to the secret for runs.