ci(gitlab-ci): fix rules for container rebuilds

.gitlab-ci.yml

@@ -89,7 +89,10 @@ setup:containers:frontend: &containers-frontend
   rules:
     - changes:
         paths:
-          - ${FRONTEND_IMAGE_DEPENDENCIES}
+          - docker/frontend/Dockerfile
+          - package.json
+          - package-lock.json
+          - webpack.config.js
   interruptible: false
 setup:containers:frontend:manual:
   <<: *containers-frontend
@@ -109,7 +112,10 @@ setup:containers:backend: &containers-backend
   rules:
     - changes:
         paths:
-          - ${BACKEND_IMAGE_DEPENDENCIES}
+          - docker/backend/Dockerfile
+          - package.yaml
+          - stack.yaml
+          - stack.yaml.lock
   interruptible: false
 setup:containers:backend:manual:
   <<: *containers-backend