Fix duplicate docs publishing

While looking at: #1230 (moved), it appeared that we publish the documentation into public and public/public.

You can see in the output of some jobs (for example, compile_dev: https://gitlab.com/gitlab-org/gitlab-docs/-/jobs/2688536303), that the minify step picks up two sets of docs). It's possible that we're actually minifying the docs into a public subdirectory, rather than just public.