ci: use node@20

Author: nikku

.github/workflows/CI.yml

@@ -5,7 +5,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest]
-        node-version: [ 16 ]
+        node-version: [ 20 ]
         integration-deps:
           - "" # as defined in package.json
           - diagram-js@8.x