fix: set response content-type for get import status requests

mentioned in commit c11ab964

mentioned in issue #629 (closed)

mentioned in merge request gitlab-org/build/CNG!940 (merged)

mentioned in merge request gitlab-org/charts/gitlab!2461 (merged)

mentioned in merge request gitlab-com/gl-infra/k8s-workloads/gitlab-com!1616 (merged)

mentioned in merge request gitlab-com/gl-infra/k8s-workloads/gitlab-com!1617 (closed)

mentioned in merge request omnibus-gitlab!6064 (merged)

mentioned in merge request gitlab-development-kit!2503 (merged)