Update docs pipeline to use new image

What does this MR do?

We started to use versioning for the docs lint image, which should hopefully eliminate pipeline failures in the stable branches caused by updating the the lint image. It will also make maintenance easier, as we can create a new image for testing without affecting current pipelines, and can roll out docs fixes for the new image in the same MR as the pipeline update itself.

Tested with a fake docs commit to trigger the job in https://gitlab.com/gitlab-org/gitlab/-/jobs/710777683 (commit since removed to allow merging).

Related to gitlab-docs#768 (closed)