ci: use node v20 for lighthouse

Author: kamilmysliwiec

.github/workflows/lighthouse.yml

@@ -3,18 +3,18 @@ name: Lighthouse
 on:
   pull_request:
     paths-ignore:
-    - 'content/**/*.md'
+      - 'content/**/*.md'
 
 jobs:
   build:
     runs-on: ubuntu-latest
 
     steps:
       - uses: actions/checkout@v4
-      - name: Use Node.js 16.x
+      - name: Use Node.js 20.x
         uses: actions/setup-node@v3
         with:
-          node-version: 16.x
+          node-version: 20.x
       # Build needs around 400 seconds on Netlify.
       # We can not rely on "Waiting for 200", since the user
       # might push another commit to an existing PR, meaning