CI: Cancel previous workflow runs on PRs

Author: kateinoigakukun

.github/workflows/test.yml

@@ -3,6 +3,9 @@ on:
   pull_request:
   push:
     branches: [main]
+concurrency:
+  group: ${{ github.workflow }} / ${{ startsWith(github.event_name, 'pull') && github.ref_name || github.sha }}
+  cancel-in-progress: ${{ startsWith(github.event_name, 'pull') }}
 jobs:
   test:
     name: Build and Test