fix(tests,webhooks): fix test assertions and webhook API structure

ts/bunq.classes.webhook.ts

@@ -23,10 +23,8 @@ export class BunqWebhook {
     const response = await this.bunqAccount.getHttpClient().post(
       `/v1/user/${this.bunqAccount.userId}/monetary-account/${monetaryAccount.id}/notification-filter-url`,
       {
-        notification_filter_url: {
-          category: 'MUTATION',
-          notification_target: url
-        }
+        category: 'MUTATION',
+        notification_target: url
       }
     );
 
@@ -107,9 +105,7 @@ export class BunqWebhook {
     await this.bunqAccount.getHttpClient().put(
       `/v1/user/${this.bunqAccount.userId}/monetary-account/${monetaryAccount.id}/notification-filter-url/${webhookId}`,
       {
-        notification_filter_url: {
-          notification_target: newUrl
-        }
+        notification_target: newUrl
       }
     );
   }