fix: bump preview workflow to node 20

Author: thejustinwalsh

.github/workflows/preview.yml

@@ -15,7 +15,7 @@ jobs:
       - uses: actions/checkout@v4
       - uses: actions/setup-node@v4
         with:
-          node-version: '16.x'
+          node-version: '20.x'
           registry-url: 'https://registry.npmjs.org'
           scope: '@ts-defold'
       - run: npm install