fix deprecation warning
fix deprecation warning

fixes same deprecation as 8b8cb26f1d852a234e8fa0c964912332744ad7a6

gds-attic/content-planner,alphagov/content-planner,gds-attic/content-planner,alphagov/content-planner,bitzesty/content-planner,bitzesty/content-planner,gds-attic/content-planner,alphagov/content-planner,bitzesty/content-planner,gds-attic/content-planner,alphagov/content-planner