add Node 20 to CI matrix

Author: JLHwung

.github/workflows/ci.yml

@@ -11,7 +11,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, windows-latest]
-        node-version: [14, 16, 18]
+        node-version: [14, 16, 18, 20]
         webpack-version: ['5']
         include:
           - node-version: "14.15.0" # The minimum supported node version