enable manual trigering'

Author: mmcky

.github/workflows/ci.yml

@@ -1,5 +1,7 @@
 name: Build Project [using jupyter-book]
-on: [pull_request]
+on: 
+  pull_request:
+  workflow_dispatch:
 jobs:
   preview:
     runs-on: "runs-on=${{ github.run_id }}/family=g4dn.xlarge/image=quantecon_ubuntu2404/disk=large"