fix(handlers): enable cross repository blob mounts without FS mirroring

mentioned in commit 6d064041

mentioned in issue #435 (closed)

mentioned in merge request gitlab-org/build/CNG!737 (merged)

mentioned in merge request omnibus-gitlab!5542 (merged)

mentioned in merge request gitlab-com/gl-infra/k8s-workloads/gitlab-com!1134 (merged)

mentioned in merge request gitlab-com/gl-infra/k8s-workloads/gitlab-com!1135 (merged)

mentioned in merge request gitlab-org/charts/gitlab!2139 (merged)

mentioned in merge request gitlab-development-kit!2385 (merged)