chore: replaces use of legacy livechat:saveCustomFields with new endpoint in api test helpers

apps/meteor/tests/data/livechat/custom-fields.ts

@@ -1,7 +1,7 @@
 import type { ILivechatCustomField } from '@rocket.chat/core-typings';
 import type { Response } from 'supertest';
 
-import { credentials, request, methodCall, api } from '../api-data';
+import { credentials, request, api } from '../api-data';
 
 type ExtendedCustomField = Omit<ILivechatCustomField, '_id' | '_updatedAt'> & { field: string };
 
@@ -19,21 +19,14 @@ export const createCustomField = (customField: ExtendedCustomField): Promise<Ext
 					resolve(res.body.customField);
 				} else {
 					void request
-						.post(methodCall('livechat:saveCustomField'))
-						.send({
-							message: JSON.stringify({
-								method: 'livechat:saveCustomField',
-								params: [null, customField],
-								id: 'id',
-								msg: 'method',
-							}),
-						})
+						.post(api('livechat/custom-fields.save'))
 						.set(credentials)
+						.send({ customFieldId: null, customFieldData: customField })
 						.end((err: Error, res: Response): void => {
 							if (err) {
 								return reject(err);
 							}
-							resolve(res.body);
+							resolve(res.body.customField);
 						});
 				}
 			});