chore(gitlab-ci): add .stack-work to stack cache

.gitlab-ci.yml

@@ -87,11 +87,13 @@ backend dependencies:
       key: default-stack
       paths:
         - .stack/
+        - .stack-work/
   script:
     - make backend-dependencies-prod
   artifacts:
     paths:
       - .stack/
+      - .stack-work/
 
 frontend build:
   stage: build
@@ -109,6 +111,7 @@ frontend build:
       - static/
       - config/webpack.yml
 
+# TODO: .stack-work cache not working
 backend build:
   stage: build
   cache: