Update markdownlint and Vale for project (!2417) · Merge requests · GitLab.org / GitLab Development Kit · GitLab

What does this Merge Request do and why?

Make use of new linting image from: gitlab-docs!2422 (merged).

CC @toon @ashmckenzie

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.