[Feature] add coverage for Set New Architecture flow when second QuickPick is cancelled

[EmmaYuan1015]

Background

In the “Set React Native New Architecture” command flow, current tests cover the case where the platform QuickPick is cancelled, but they do not cover the branch where the platform is selected and the second QuickPick (true/false) is cancelled.

Problem

Missing this branch creates two risks:

Regressions in cancellation handling may go unnoticed.
The command could accidentally perform side effects (file writes or command execution) after cancellation.
Expected Behavior
If the user selects a platform and then cancels the second QuickPick:

The command should return immediately.
No configuration file should be written.
No side-effect command should be executed (for example, pod install).

Proposed Fix

Add a unit test that simulates:

First QuickPick returns a valid platform (for example, Android).
Second QuickPick returns undefined.
Assertions verify no file write and no spawned command.

Acceptance Criteria

The new test is added and passes.
Existing covered scenarios remain unchanged.
Cancellation behavior is protected against future regressions.