ci: publish backend release tags to zot

.woodpecker/release-backend.yml

@@ -14,7 +14,7 @@ steps:
       - node scripts/check-api-contract.mjs "$CI_COMMIT_TAG"
 
   publish-backend:
-    image: woodpeckerci/plugin-docker-buildx:2
+    image: woodpeckerci/plugin-docker-buildx:5.0.0
     privileged: true
     settings:
       context: .