fix(utils): medusa internal service returned data should match typings (#12715)

FIXES SUP-1824

**What**
The medusa internal service update should always return the data in the expected shape described by the interface. The medusa service should not have to handle the reshapre

packages/modules/fulfillment/src/services/fulfillment-module-service.ts

@@ -2021,9 +2021,11 @@ export default class FulfillmentModuleService
       })
     }
 
-    const result = await this.baseRepository_.serialize(fulfillment)
+    const result = await this.baseRepository_.serialize<FulfillmentDTO>(
+      fulfillment
+    )
 
-    return Array.isArray(result) ? result[0] : result
+    return result
   }
 
   async retrieveFulfillmentOptions(