fix Activity schema error

packages/app/src/server/models/activity.ts

@@ -35,7 +35,7 @@ module.exports = function(crowi: Crowi) {
     user: {
       type: Schema.Types.ObjectId,
       ref: 'User',
-      index: true,
+      // index: true,
       require: true,
     },
     targetModel: {

packages/app/src/server/service/in-app-notification.ts

@@ -84,8 +84,8 @@ export default class InAppNotificationService {
           { path: 'target' },
           { path: 'activities', populate: { path: 'user' } },
         ],
-      });
-
+      },
+    );
 
     return paginatedInAppNotificationResult;
   }