Update Node.js version in GitHub Actions workflow

Author: kateinoigakukun

.github/workflows/deploy-pages.yml

@@ -15,7 +15,7 @@ jobs:
       - name: Setup Node.js
         uses: actions/setup-node@v4
         with:
-          node-version: '14'
+          node-version: '20'
 
       - run: npm ci
       - run: npm run build