apply correct s6 overlay

.github/workflows/build.yaml

@@ -122,10 +122,10 @@ jobs:
       fail-fast: false
       matrix:
         job:
-          - { name: "amd64",   docker_platform: "linux/amd64" }
-          - { name: "arm64v8", docker_platform: "linux/arm64" }
-          - { name: "armv7",   docker_platform: "linux/arm/v7" }
-          - { name: "i386",    docker_platform: "linux/386" }
+          - { name: "amd64",   docker_platform: "linux/amd64",  s6_platform: "x86_64" }
+          - { name: "arm64v8", docker_platform: "linux/arm64",  s6_platform: "aarch64" }
+          - { name: "armv7",   docker_platform: "linux/arm/v7", s6_platform: "armhf" }
+          - { name: "i386",    docker_platform: "linux/386",    s6_platform: "i686" }
 
     steps:
 
@@ -174,6 +174,8 @@ jobs:
           context: "./docker"
           platforms: ${{ matrix.job.docker_platform }}
           push: true
+          build-args: |
+            S6_ARCH=${{ matrix.job.s6_platform }}
           tags: |
             ${{ secrets.DOCKER_IMAGE }}:${{ env.LATEST_TAG }}-${{ matrix.job.name }}
             ${{ secrets.DOCKER_IMAGE }}:${{ env.GIT_TAG }}-${{ matrix.job.name }}

docker/Dockerfile

@@ -1,13 +1,14 @@
 FROM busybox:stable
 
 ARG S6_OVERLAY_VERSION=3.1.0.1
+ARG S6_ARCH=x86_64
 ADD https://github.com/just-containers/s6-overlay/releases/download/v${S6_OVERLAY_VERSION}/s6-overlay-noarch.tar.xz /tmp
-ADD https://github.com/just-containers/s6-overlay/releases/download/v${S6_OVERLAY_VERSION}/s6-overlay-x86_64.tar.xz /tmp
+ADD https://github.com/just-containers/s6-overlay/releases/download/v${S6_OVERLAY_VERSION}/s6-overlay-${S6_ARCH}.tar.xz /tmp
 RUN \
   tar -C / -Jxpf /tmp/s6-overlay-noarch.tar.xz && \
-  tar -C / -Jxpf /tmp/s6-overlay-x86_64.tar.xz && \
+  tar -C / -Jxpf /tmp/s6-overlay-${S6_ARCH}.tar.xz && \
   rm /tmp/s6-overlay*.tar.xz
-  
+
 COPY rootfs /
 
 ENV RELAY relay.example.com