fix(handlers): do not write manifests on HEAD requests

mentioned in commit f0ab1a81

mentioned in issue #1209 (closed)

mentioned in merge request gitlab-org/build/CNG!1747 (merged)

mentioned in merge request omnibus-gitlab!7456 (merged)

mentioned in merge request gitlab-org/charts/gitlab!3644 (merged)

mentioned in merge request gitlab-com/gl-infra/k8s-workloads/gitlab-com!3433 (merged)

mentioned in merge request gitlab-com/gl-infra/k8s-workloads/gitlab-com!3434 (merged)

mentioned in merge request gitlab-com/gl-infra/k8s-workloads/gitlab-com!3435 (merged)