chore: update CI Node versions

This still supports Node 16, but requires Node 18 to build.

.github/workflows/node.js.yml

@@ -16,7 +16,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        node: [16.x, 18.x]
+        node: [18.x, 20.x]
     steps:
       - uses: actions/checkout@v3
       - name: Install Node.js ${{ matrix.node }}