Fix specifying a non-default ref when requesting an archive using the legacy URL

What does this MR do?

Fixes the behaviour of URLs like https://gitlab.com/gitlab-org/gitlab-pages/repository/archive.tar.gz?ref=v0.7.0 so they return the requested reference, instead of master.

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

This is a regression introduced in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/17225 that subtly breaks a range of automated release processes, leading to people getting the wrong code. At least one downstream project that we know of has been affected (AUR builds of git-latexdiff).

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Review
  • Has been reviewed by Backend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

/cc @jramsay

Closes #45507 (closed)