It should be possible to build MRs from forks that the API user doesn’t have access to

### What feature do you want to see added?

When scanning MRs, I get the following message if the user isn’t allowed to access the fork:

```
Ignoring merge requests as source project not found, Please check permission on source repo...
```

However, I don’t think there is any requirement for the builder to have access to the fork. The commits (and their authors) are also available on the target repo (for example under the `refs/merge-requests/*/head` refs).

### Upstream changes

Unsure

### Are you interested in contributing this feature?

Maybe, with guidance