ADD: run github action periodically

Author: ctgk

.github/workflows/run-notebooks.yaml

@@ -8,6 +8,9 @@ on:
     branches: [ main, develop ]
   pull_request:
     branches: [ main, develop ]
+  schedule:
+    # run every month on 6th day
+    - cron: '0 0 6 * *'
 
 jobs:
   jupyter-notebooks: