ci: Add node 18.x to build/tests (#548)

Author: rmi22186

.github/workflows/higgs-shop-sample-app-pull-request.yml

@@ -21,7 +21,7 @@ jobs:
         strategy:
             matrix:
                 os: [windows-latest, ubuntu-latest, macos-latest]
-                node-version: [16.x, 17.x]
+                node-version: [16.x, 17.x, 18.x]
         steps:
             - name: Checkout
               uses: actions/checkout@v2