Add `HEAD` handlers for repo index file for debian package registry. Resolves #11488 Co-authored-by: sarge <ephemeralsarge@example.com> Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/11489 Reviewed-by: Gusted <gusted@noreply.codeberg.org> Co-authored-by: sarge <sarge@noreply.codeberg.org> Co-committed-by: sarge <sarge@noreply.codeberg.org>