ci: build workflow dispatch instead of push

Author: Palke

.github/workflows/publish-cdn.yml

@@ -2,9 +2,7 @@ name: Publish CDN artifacts (versioned) to S3
 run-name: Publish CDN artifacts - versioned by @${{ github.actor }}
 
 on:
-  push:
-    branches:
-      - main
+  workflow_dispatch:
 
 concurrency:
   group: deploy-${{ github.ref }}