sinks/gitlabmentions.py: Gracefully handle private projects
We'll get a "404 Project Not Found" error when trying to retrieve a
merge request for a private project. Handle this gracefully.
How to register an account on GitLab. To prevent spam, new accounts are locked until approved by an admin or the approver bot. You can also file an unlock request to expedite access.
Support: mw:GitLab, how to host a project on GitLab, #wikimedia-gitlab on libera.chat, #GitLab on Phabricator.
We'll get a "404 Project Not Found" error when trying to retrieve a
merge request for a private project. Handle this gracefully.