api: fix ValidatingAdmissionPolicyList json tag

This change make api-server not omity the field `item` of
ValidatingAdmissionPolicyList when ValidatingAdmissionPolicy is empty.
So kubetl will print ValidatingAdmissionPolicyList correctly when ValidatingAdmissionPolicy is empty.

Signed-off-by: xyz-li <hui0787411@163.com>

staging/src/k8s.io/api/admissionregistration/v1/types.go

@@ -203,7 +203,7 @@ type ValidatingAdmissionPolicyList struct {
 	// +optional
 	metav1.ListMeta `json:"metadata,omitempty" protobuf:"bytes,1,opt,name=metadata"`
 	// List of ValidatingAdmissionPolicy.
-	Items []ValidatingAdmissionPolicy `json:"items,omitempty" protobuf:"bytes,2,rep,name=items"`
+	Items []ValidatingAdmissionPolicy `json:"items" protobuf:"bytes,2,rep,name=items"`
 }
 
 // ValidatingAdmissionPolicySpec is the specification of the desired behavior of the AdmissionPolicy.