test: stabilize memory async search close

src/memory/manager.async-search.test.ts

@@ -87,6 +87,7 @@ describe("memory search async sync", () => {
     });
 
     manager = await createMemoryManagerOrThrow(cfg);
+    (manager as unknown as { dirty: boolean }).dirty = true;
     await manager.search("hello");
     await vi.waitFor(() => {
       expect((manager as unknown as { syncing: Promise<void> | null }).syncing).toBeTruthy();