Run system test on Devcontainer smoke test

To confirm the files for Dev Containers are generated correctly.

.github/workflows/devcontainer-smoke-test.yml

@@ -63,7 +63,7 @@ jobs:
           imageTag: postgresql
           push: ${{ github.repository_owner == 'rails' && 'filter' || 'never' }}
           refFilterForPush: refs/heads/main
-          runCmd: bin/rails g scaffold Post && bin/rails db:migrate && bin/rails test
+          runCmd: bin/rails g scaffold Post && bin/rails db:migrate && bin/rails test && bin/rails test:system
 
       - name: Stop all containers
         run: docker ps -q | xargs docker stop