Add a workflow to verify Prettier formatting

.github/workflows/check-formatting.yml

@@ -0,0 +1,26 @@
+name: Checking formatting
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: Setup Node.JS
+        uses: actions/setup-node@v3
+        with:
+          node-version: 16.x
+          cache: 'npm'
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Verify formatting
+        run: npm run format:check

package.json

@@ -5,7 +5,9 @@
   "description": "A GitHub Action to enable Pages and extract various metadata about a site. It can also be used to configure various static site generators we support as starter workflows.",
   "main": "./dist/index.js",
   "scripts": {
-    "prepare": "ncc build src/index.js -o dist --source-map --license licenses.txt",
+    "format": "prettier --write 'src/**/*.js'",
+    "format:check": "prettier --check 'src/**/*.js'",
+    "prepare": "npm run format && ncc build src/index.js -o dist --source-map --license licenses.txt",
     "test": "jest"
   },
   "repository": {