Fix sidebar workspace list test AsyncStorage mock

fa20f313 wired AsyncStorage persistence into
activateNavigationWorkspaceSelection. The mock here returned undefined
from setItem, so the .catch() in persistLastWorkspaceRouteSelection
threw. Make get/set/removeItem return resolved promises like real
AsyncStorage.

packages/app/src/components/sidebar-workspace-list.test.tsx

@@ -37,9 +37,9 @@ import {
 
 vi.mock("@react-native-async-storage/async-storage", () => ({
   default: {
-    getItem: vi.fn(),
-    setItem: vi.fn(),
-    removeItem: vi.fn(),
+    getItem: vi.fn().mockResolvedValue(null),
+    setItem: vi.fn().mockResolvedValue(undefined),
+    removeItem: vi.fn().mockResolvedValue(undefined),
   },
 }));