Skip Docker if already pushed

ci/steps/push-docker-manifest.sh

@@ -1,6 +1,17 @@
 #!/usr/bin/env bash
 set -euo pipefail
 
+# See if this version already exists on Docker Hub.
+function version_exists() {
+  local output
+  output=$(curl --silent "https://index.docker.io/v1/repositories/codercom/code-server/tags/$VERSION")
+  if [[ $output == "Tag not found" ]]; then
+    return 1
+  else
+    return 0
+  fi
+}
+
 # Import and push the Docker image for the provided arch.
 push() {
   local arch=$1
@@ -26,6 +37,11 @@ main() {
   cd "$(dirname "$0")/../.."
   source ./ci/lib.sh
 
+  if version_exists; then
+    echo "$VERSION is already pushed"
+    return
+  fi
+
   download_artifact release-images ./release-images
   if [[ ${CI-} ]]; then
     echo "$DOCKER_PASSWORD" | docker login -u "$DOCKER_USERNAME" --password-stdin