feat: test lint issue - add agentic cli preferences (MetaMask#8933) (MetaMask#9173)

## Explanation

Follow-up to MetaMask#8933. The `does not mutate DEFAULT_AGENTIC_CLI_PREFERENCES
when coercing legacy payloads` test in
`@metamask/authenticated-user-storage` failed TypeScript and ESLint
checks after `agenticCli` was added as an optional field on
`NotificationPreferences`.

The guard now checks `result?.agenticCli` instead of only `result`, so
TypeScript narrows correctly before the test mutates
`result.agenticCli.inAppNotificationsEnabled`. No runtime or API
behavior changes.

## References

* Follow-up to MetaMask#8933

## Checklist

- [x] I've updated the test suite for new or updated code as appropriate
- [ ] I've updated documentation (JSDoc, Markdown, etc.) for new or
updated code as appropriate
- [ ] I've communicated my changes to consumers by [updating changelogs
for packages I've
changed](https://github.com/MetaMask/core/tree/main/docs/processes/updating-changelogs.md)
- [ ] I've introduced [breaking
changes](https://github.com/MetaMask/core/tree/main/docs/processes/breaking-changes.md)
in this PR and have prepared draft pull requests for clients and
consumer packages to resolve them

Author: ieow

packages/authenticated-user-storage/src/authenticated-user-storage.test.ts

@@ -229,11 +229,10 @@ describe('AuthenticatedUserStorageService', () => {
       const result = await service.getNotificationPreferences();
 
       expect(result).not.toBeNull();
-      if (!result) {
+      if (!result?.agenticCli) {
         throw new Error('Result is null');
       }
       result.agenticCli.inAppNotificationsEnabled = false;
-
       expect(DEFAULT_AGENTIC_CLI_PREFERENCES.inAppNotificationsEnabled).toBe(
         true,
       );