CI: bump node to v20 (#16)

### Changelog
None

### Description
Same reasoning as foxglove/rosmsg#51

Author: jtbandes

.github/workflows/ci.yml

@@ -20,7 +20,7 @@ jobs:
       - uses: actions/checkout@v3
       - uses: actions/setup-node@v3
         with:
-          node-version: 16.x
+          node-version: 20.x
           registry-url: https://registry.npmjs.org
           cache: yarn