Fix 'only' regex for the review-docs job
What does this MR do?
The automatic docs review job should run on docs-only branches. This MR fixes what was introduced in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/20327. Previously it would run on all branches.
I tested with my fork and this is the pipeline that was created https://gitlab.com/axil/gitlab-ce/pipelines/25107976.
Edited by Achilleas Pipinellis