Add Node 21 to CI (#1430)

Author: drwpow

.github/workflows/ci.yml

@@ -39,7 +39,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        node-version: [18.x, 20.x]
+        node-version: [18.x, 20.x, 21.x]
     steps:
       - uses: actions/checkout@v3
       - uses: actions/setup-node@v3