解决办法：参考链接：https://github.com/kubernetes/kubernetes/issues/60807
kubectl get namespace cert-manager -o json > tmp.json
then edit tmp.json and remove"kubernetes"
kubectl proxy
curl -k -H "Content-Type: application/json" -X PUT --data-binary @tmp.json http://127.0.0.1:8001/api/v1/namespaces/cert-manager/finalize