Update index.md

Environment variable derived within gitlab-ci can't be re-used by other environmnet variable

doc/user/infrastructure/index.md

@@ -121,12 +121,11 @@ to the repository.
 
    ```yaml
    variables:
-     TF_STATE: ${CI_PROJECT_NAME}
-     TF_ADDRESS: ${CI_API_V4_URL}/projects/${CI_PROJECT_ID}/terraform/state/${TF_STATE}
+     TF_ADDRESS: ${CI_API_V4_URL}/projects/${CI_PROJECT_ID}/terraform/state/${CI_PROJECT_NAME}
      TF_ROOT: ${CI_PROJECT_DIR}/environments/cloudflare/production
 
    cache:
-     key: ${TF_STATE}
+     key: ${CI_PROJECT_NAME}
      paths:
        - ${TF_ROOT}/.terraform
    ```