fix the bug that update-vendor.sh reports error when grep match failed

Author: SataQiu

hack/update-vendor.sh

@@ -298,7 +298,7 @@ go mod tidy >>"${LOG_FILE}" 2>&1
 
 # disallow transitive dependencies on k8s.io/kubernetes
 loopback_deps=()
-kube::util::read-array loopback_deps < <(go mod graph | grep ' k8s.io/kubernetes')
+kube::util::read-array loopback_deps < <(go mod graph | grep ' k8s.io/kubernetes' || true)
 if [[ -n ${loopback_deps[*]:+"${loopback_deps[*]}"} ]]; then
   kube::log::error "Disallowed transitive k8s.io/kubernetes dependencies exist via the following imports:"
   kube::log::error "${loopback_deps[@]}"