workflow: fix publish-docs workflow error (#398)

Fix errors like https://github.com/tmc/langchaingo/actions/runs/7094309081

Author: eliben

.github/workflows/publish-docs.yaml

@@ -1,7 +1,9 @@
 name: Deploy to GitHub Pages
 
 on:
-  push: main
+  push:
+    branches:
+      - main
 
 permissions:
   contents: read