GitHub Actions: Allow manually trigger CI workflows (#6)

Author: tangrufus

.github/workflows/ci.yml

@@ -7,6 +7,7 @@ on:
   pull_request:
     branches:
       - main
+  workflow_dispatch:
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.run_id }}