Dockerfile: Labels don't show up in final image

The Dockerfile adds some labels for podman-auto-update which I'd like to try using eventually. It looks to me like those labels don't end up in the final image, because they are declared in the wrong section of the multi-stage build.

$ podman image inspect containers.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake:latest 
[
     {
          "Id": "124127d241f548560791fb6df22f7c67b65634c2d247668d2c38c97cfe199c00",
[...]
          "Labels": null,

I created a patch to fix that, here's the result on a local build:

$ podman image inspect localhost/snowflake-testbuild-otherlabel:latest 
[...]
          "Labels": {
               "io.buildah.version": "1.40.1",
               "io.containers.autoupdate": "registry",
               "org.opencontainers.image.authors": "anti-censorship-team@lists.torproject.org"
          },

0001-Fix-missing-labels-in-Docker-image.patch

(Sending a patch here because I was unable to create a merge request, I'll create another issue about that.)