ci: Check if files are formatted

.github/workflows/CI.yaml

@@ -0,0 +1,25 @@
+# SPDX-FileCopyrightText: 2025 Shun Sakai
+#
+# SPDX-License-Identifier: CC0-1.0
+
+name: CI
+
+on:
+  pull_request:
+  push:
+    branches:
+      - "master"
+
+jobs:
+  prettier:
+    name: Prettier
+    runs-on: ubuntu-24.04
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v5
+      - name: Setup Node.js environment
+        uses: actions/setup-node@v5
+        with:
+          node-version: 22
+      - name: Run formatter in check mode
+        run: npx prettier -c "**.{md,yaml,yml}"

.github/workflows/actionlint.yaml

@@ -25,7 +25,7 @@ jobs:
         uses: actions/checkout@v5
         with:
           persist-credentials: false
-      - name: Check no lint warnings
+      - name: Run linter
         uses: docker://rhysd/actionlint:latest
         with:
           args: -color -verbose