Update gitlab-dangerfiles and remove a small workaround

What does this Merge Request do and why?

This fixes the problem when there were two categories including one nil:

Depends on https://gitlab.com/gitlab-org/gitlab-dangerfiles/-/merge_requests/51.

Merge Request checklist

• This change is backward compatible. If not, please include steps to communicate to our users.
• Tests added for new functionality. If not, please raise Issue to follow-up.
• Documentation added/updated, if needed.
• gdk doctor test added, if needed.
• Add the ~highlight label if this MR should be included in the CHANGELOG.md.

Fixes #1265 (closed).