Update gitlab-docs to Ruby 3
This is one of the projects which requires Ruby to be updated: https://gitlab.com/gitlab-org/gitlab-docs/-/blob/main/.ruby-version
docs-lint links
in GitLab uses the image from https://gitlab.com/gitlab-org/gitlab-docs/-/blob/main/.gitlab-ci.yml#L241.
It seems that it shouldn't block our Ruby 3 transition for GitLab (we may still use the docs-lint image with 2.7).
If that is so, we could update gitlab-docs
later (after having a CI pipeline with Ruby 3 in GitLab).
Edited by Aleksei Lipniagov