reintroduce GIT_SHA to container

.github/workflows/docker-publish.yml

@@ -67,6 +67,8 @@ jobs:
           # NB: The `git_push_tag: true` option does not work as expected, so we put the sha in `image_tag`:
           # https://github.com/whoan/docker-build-with-cache-action/issues/72
           image_tag: latest,${{ github.sha }},${{ steps.vars.outputs.sha_short }}
+          # NB: Inject the Git SHA into the container so the servers can emit their own version:
+          build_extra_args: "--build-arg GET_SHA=${{ github.sha }}"
 
       # - name: Build image
       #   run: |