Add npm i to deploy workflow

Author: wilwade

.github/workflows/deploy-gh-pages.yaml

@@ -18,6 +18,14 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
 
+      - name: Use Node.js 🐰
+        uses: actions/setup-node@v4
+        with:
+          node-version: 20
+
+      - name: Install Node Modules 💾
+        run: npm ci
+
       - name: Set up mdBook 📚
         uses: ./.github/workflows/common/set-up-mdbook
         with: