magnum: Fix trustee creation after ansible-collections-openstack bump

Change-Id: I54e68a3002d69f7b1be2704259c6a072f81aa586

ansible/roles/magnum/tasks/register.yml

@@ -42,7 +42,7 @@
     container_engine: "{{ kolla_container_engine }}"
     module_name: "os_user_role"
     module_args:
-      domain: "{{ trustee_domain.id }}"
+      domain: "{{ trustee_domain.domain.id }}"
       user: "{{ magnum_trustee_domain_admin }}"
       role: "admin"
       auth: "{{ openstack_magnum_auth }}"