Extracting the variable substitution to a 'variables' directive

.gitlab-ci.yml

@@ -29,9 +29,11 @@ review:
   extends: .deploy
   rules:
     - if: $CI_COMMIT_BRANCH != $CI_DEFAULT_BRANCH
+  variables:
+    ROOT_RELATIVE_NAMESPACE: "${CI_PROJECT_NAMESPACE#$CI_PROJECT_ROOT_NAMESPACE}"
   environment:
     name: "review $CI_COMMIT_BRANCH"
-    url: "https://${CI_PROJECT_ROOT_NAMESPACE}.${CI_PAGES_DOMAIN}/-${CI_PROJECT_NAMESPACE#$CI_PROJECT_ROOT_NAMESPACE}/${CI_PROJECT_NAME}/-/jobs/$CI_JOB_ID/artifacts/public/index.html"
+    url: "https://${CI_PROJECT_ROOT_NAMESPACE}.${CI_PAGES_DOMAIN}/-${ROOT_RELATIVE_NAMESPACE}/${CI_PROJECT_NAME}/-/jobs/$CI_JOB_ID/artifacts/public/index.html"
 
 # Deploy to GitLab Pages for pushes on the default branch
 pages: