Remove /tmp prefix that diverges from source

What does this MR do and why?

The internal anchors check runs

Follow-up to #1723 (comment 1602050730)

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Configure a local GitLab Docs environment: https://gitlab.com/gitlab-org/gitlab-docs/-/blob/main/doc/setup.md.

2. Break some anchors links.

3. Run the anchor link check:

   make internal-anchors-check

4. Check that the output matches the following:

   • If the anchor link was in the runner repo, it should be prefixed with docs/.
   • In all other repos, it should be prefixed with doc/.

Merge request acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this merge request.

Closes #1723