Enable workflow_dispatch option in Actions workflow

Author: yasulab

.github/workflows/ci.yml

@@ -6,6 +6,9 @@ on:
   pull_request:
     branches:
       - "*"
+  # Allows you to run this workflow manually from the Actions tab
+  # https://docs.github.com/en/actions/managing-workflow-runs/manually-running-a-workflow
+  workflow_dispatch:
 
 jobs:
   test: