Automatically cancel outdated CI runs on PR

Author: taiki-e

.github/workflows/ci.yml

@@ -17,6 +17,14 @@ env:
   RUSTFLAGS: -D warnings
   RUSTUP_MAX_RETRIES: 10
 
+defaults:
+  run:
+    shell: bash
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.sha }}
+  cancel-in-progress: true
+
 jobs:
   build:
     name: Build on Linux