Use Node 20 for Gatsby build

Author: alainrobert

.github/workflows/main.yml

@@ -11,7 +11,7 @@ jobs:
       - uses: actions/checkout@v3
       - uses: actions/setup-node@v3
         with:
-          node-version: '18'
+          node-version: '20'
       - run: npm install
       - run: npm run build
         env: