ci: check changed-file formatting (#557)

.github/workflows/test.yml

@@ -13,6 +13,31 @@ concurrency:
   cancel-in-progress: true
 
 jobs:
+  format:
+    runs-on: ubuntu-latest
+    timeout-minutes: 20
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v7
+        with:
+          fetch-depth: 0
+
+      - name: Setup Node
+        uses: actions/setup-node@v7
+        with:
+          node-version: '24'
+          cache: yarn
+          cache-dependency-path: yarn.lock
+
+      - name: Install dependencies
+        run: yarn --frozen-lockfile
+
+      - name: Check changed-file formatting
+        env:
+          BASE_SHA: ${{ github.event.pull_request.base.sha }}
+          HEAD_SHA: ${{ github.event.pull_request.head.sha }}
+        run: yarn format:check --base "$BASE_SHA" --head "$HEAD_SHA"
+
   lint:
     runs-on: ubuntu-latest
     timeout-minutes: 20