Limit the publish_website.yml work-flow to only the master branch (issue 16369)

This is a tentative patch, based on https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#using-filters

.github/workflows/publish_website.yml

@@ -1,5 +1,8 @@
 name: Publish website
-on: [push]
+on:
+  push:
+    branches:
+      - master
 permissions:
   contents: read