chore: run CI on Node 21 (#602)

Author: SimenB

.github/workflows/nodejs.yml

@@ -16,7 +16,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        node-version: [16.x, 18.x, 20.x]
+        node-version: [16.x, 18.x, 20.x, 21.x]
         os: [ubuntu-latest, windows-latest, macOS-latest]
 
     runs-on: ${{ matrix.os }}