Use Node 18.x in CI tests

.github/workflows/karma-tests.yml

@@ -17,7 +17,7 @@ jobs:
 
     strategy:
       matrix:
-        node-version: [16.x]
+        node-version: [18.x]
         # See supported Node.js release schedule at https://nodejs.org/en/about/releases/
 
     steps: