update node version

Author: clarasb

.github/workflows/publish-frontend.yml

@@ -108,7 +108,7 @@ jobs:
       - name: Set up Node.js
         uses: actions/setup-node@v4
         with:
-          node-version: '18.x'
+          node-version: '20.x'
           registry-url: 'https://registry.npmjs.org'
           cache: 'npm'
           cache-dependency-path: chartlets.js/package-lock.json