ci: add format-check job

Author: p-chan

.github/workflows/ci.yml

@@ -5,6 +5,20 @@ on:
   - pull_request
 
 jobs:
+  format-check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Use Node.js
+        uses: actions/setup-node@v3
+        with:
+          node-version: 16
+          cache: 'yarn'
+      - name: Install dependencies
+        run: yarn
+      - name: Format check
+        run: yarn format:check
+
   build:
     runs-on: ubuntu-latest
     steps: