Enable manual github action runs (#23836)

.github/workflows/runtime-sync.yml

 name: AspNetCore-Runtime Code Sync
 on:
-  # Test this script using on: push
-  # push:
+  # Manual run
+  workflow_dispatch:
   schedule:
     # * is a special character in YAML so you have to quote this string
     # https://help.github.com/en/actions/automating-your-workflow-with-github-actions/events-that-trigger-workflows#scheduled-events-schedule