gitlab: set cache and config dir in top-level file (#39829)

share/spack/gitlab/cloud_pipelines/.gitlab-ci.yml

@@ -1,5 +1,9 @@
 stages: [ "generate", "build", "publish" ]
 
+variables:
+  SPACK_DISABLE_LOCAL_CONFIG: "1"
+  SPACK_USER_CACHE_PATH: "${CI_PROJECT_DIR}/tmp/_user_cache/"
+
 default:
   image: { "name": "ghcr.io/spack/e4s-ubuntu-18.04:v2021-10-18", "entrypoint": [""] }
 
@@ -65,8 +69,6 @@ default:
 .base-job:
   variables:
     SPACK_BUILDCACHE_DESTINATION: "s3://spack-binaries/${CI_COMMIT_REF_NAME}/${SPACK_CI_STACK_NAME}"
-    SPACK_DISABLE_LOCAL_CONFIG: "1"
-    SPACK_USER_CACHE_PATH: "${CI_PROJECT_DIR}/tmp/_user_cache/"
   rules:
     - if: $CI_COMMIT_REF_NAME == "develop"
       # Pipelines on develop only rebuild what is missing from the mirror