chore(gitlab-ci): use STACK_ROOT for cache

.gitlab-ci.yml

@@ -28,6 +28,8 @@ variables:
     extra-substituters = https://cache.iog.io
     extra-trusted-public-keys = hydra.iohk.io:f/Ea+s+dFdN+3Y/G+FDgSq+a5NEWhJGzdjvKNGv0/EQ=
 
+  STACK_ROOT: "${CI_PROJECT_DIR}/.stack"
+
 stages:
   - setup
   - lint
@@ -98,15 +100,14 @@ backend dependencies:
     - &stack-cache
       key: default-stack
       paths:
-        - ${HOME}/.stack
-        - .stack-work
+        - .stack
   script:
     - echo ${LC_ALL} ${LANG}
     - make backend-dependencies-prod
   before_script: *nix-before
   artifacts:
     paths:
-      - ${HOME}/.stack
+      - .stack
     name: "${CI_JOB_NAME}-${CI_COMMIT_SHORT_SHA}"
     expire_in: "1 day"
   retry: 2