workflow: fix proxmox-backup-server arch used

Author: ayufan

dockerfiles/Dockerfile.build

@@ -60,9 +60,10 @@ COPY --from=builder /src/release/ /release/
 
 # Bundle server
 ARG VERSION
+ARG ARCH=
 ADD /scripts/release /src/scripts/release
 RUN /src/scripts/release/apt-install.bash --gen /release/install /release proxmox-backup-server
-RUN /src/scripts/release/bundle-tgz.bash /proxmox-backup-server-${VERSION}-${DOCKER_ARCH:-dev}.tgz /release/.
+RUN /src/scripts/release/bundle-tgz.bash /proxmox-backup-server-${VERSION}-${ARCH:-dev}.tgz /release/.
 
 #=================================