Fix host tests

Author: FadhlanR

packages/host/app/services/matrix-service.ts

@@ -2,6 +2,7 @@ import type Owner from '@ember/owner';
 import type RouterService from '@ember/routing/router-service';
 import { debounce } from '@ember/runloop';
 import Service, { service } from '@ember/service';
+import { buildWaiter } from '@ember/test-waiters';
 import { cached, tracked } from '@glimmer/tracking';
 
 import { restartableTask, task } from 'ember-concurrency';
@@ -122,6 +123,7 @@ const SLIDING_SYNC_LIST_RANGE_SIZE = 10;
 const SLIDING_SYNC_LIST_TIMELINE_LIMIT = 1;
 
 const realmEventsLogger = logger('realm:events');
+const waiter = buildWaiter('matrix-service:waiter');
 
 export type OperatorModeContext = {
   submode: Submode;
@@ -1181,6 +1183,7 @@ export default class MatrixService extends Service {
     }
 
     this.timelineLoadingState.set(roomId, true);
+    let token = waiter.beginAsync();
     try {
       while (room.oldState.paginationToken != null) {
         await this.client.scrollback(room);
@@ -1209,6 +1212,7 @@ export default class MatrixService extends Service {
       });
     } finally {
       this.timelineLoadingState.set(roomId, false);
+      waiter.endAsync(token);
     }
   });