Fix the nginx cache snippets - I'd missed the file nesting somehow. Tested on a debian:bookworm image with nginx-full installed, checked that we could pull an arbitrary external site, as well as S3, as well as GitLab artifacts. Signed-off-by: Daniel Stone <daniels@collabora.com> Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/34341>