ci: Require a missing file in review-cleanup

What does this MR do and why?

This fixes a problem that I noticed in the latest scheduled pipelines: https://gitlab.com/gitlab-org/gitlab/-/jobs/1882193040

review-cleanup shows an error but continues when the namespace to clean up cannot be found:

$ delete_release
** Checking if review-fix-review-yclzl4 exists in the review-fix-review-yclzl4 namespace... **
Previous deployment for review-fix-review-yclzl4 NOT found.
$ delete_namespace
** Checking if review-fix-review-yclzl4 exists... **
Namespace review-fix-review-yclzl4 NOT found.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

.gitlab/ci/review-apps/main.gitlab-ci.yml

@@ -105,4 +105,4 @@ review-stop:
   stage: deploy
   needs: []
   script:
-    - delete_k8s_release_namespace
+    - delete_namespace