fix: restore manifest delete webhook notifications on the new code path

mentioned in commit 444f92f1

mentioned in issue #728 (closed)

mentioned in merge request gitlab-org/build/CNG!1073 (merged)

mentioned in merge request gitlab-com/gl-infra/k8s-workloads/gitlab-com!1950 (merged)

mentioned in merge request gitlab-com/gl-infra/k8s-workloads/gitlab-com!1958 (merged)

mentioned in merge request gitlab-development-kit!2964 (merged)