Update Dockerfile

Dockerfile

-ARG DOCKER_REGISTRY=registry.cyberbrain.pw
-FROM $DOCKER_REGISTRY/tools/docker/git-sync:latest
+ARG GIT_SYNC_VERSION=v3.6.9
+
+FROM registry.k8s.io/git-sync/git-sync:${GIT_SYNC_VERSION} AS runtime
 
 ENV GIT_SYNC_ROOT='/tmp/git' \
     GIT_SYNC_DEST='sync' \
@@ -27,3 +28,5 @@ RUN set -ex \
 VOLUME ["/sync"]
 
 USER 65533:65533
+
+FROM runtime AS release