ci(ios): reject previous TestFlight build waiting for review (MetaMask#28219)

## **Description**

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also include relevant motivation and context. Have in mind the following
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1. What is the reason for the change?
2. What is the improvement/solution?
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The nightly iOS TestFlight uploads fail when a previous build in the
same version train is already waiting for beta review. Apple only allows
one build per version to be in beta review at a time, causing a
`Spaceship::UnexpectedResponse` error that fails the CI job even though
the IPA uploaded successfully.

This adds `reject_build_waiting_for_review: true` to the
`upload_to_testflight` Fastlane action, which automatically rejects the
previous build's pending review submission before submitting the new
one. This ensures back-to-back builds (e.g. nightly exp then rc) can
always distribute to external testers without manual intervention.
Previously approved builds remain available in TestFlight — only the
pending review submission is cancelled.

## **Changelog**

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`CHANGELOG entry: Added a new tab for users to see their NFTs`
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CHANGELOG entry: null

## **Related issues**

Fixes:

## **Manual testing steps**

```gherkin
Feature: TestFlight upload with reject_build_waiting_for_review

  Scenario: nightly build uploads when previous build is waiting for review
    Given a previous iOS build is waiting for beta review in App Store Connect

    When a new nightly build triggers the upload-to-testflight workflow
    Then the previous build's review submission should be rejected
    And the new build should be uploaded and submitted for beta review
    And the workflow should complete successfully
```

## **Screenshots/Recordings**

### **Before**

N/A

### **After**

N/A

## **Pre-merge author checklist**

- [x] I've followed [MetaMask Contributor
Docs](https://github.com/MetaMask/contributor-docs) and [MetaMask Mobile
Coding
Standards](https://github.com/MetaMask/metamask-mobile/blob/main/.github/guidelines/CODING_GUIDELINES.md).
- [x] I've completed the PR template to the best of my ability
- [x] I've included tests if applicable
- [x] I've documented my code using [JSDoc](https://jsdoc.app/) format
if applicable
- [x] I've applied the right labels on the PR (see [labeling
guidelines](https://github.com/MetaMask/metamask-mobile/blob/main/.github/guidelines/LABELING_GUIDELINES.md)).
Not required for external contributors.

## **Pre-merge reviewer checklist**

- [ ] I've manually tested the PR (e.g. pull and build branch, run the
app, test code being changed).
- [ ] I confirm that this PR addresses all acceptance criteria described
in the ticket it closes and includes the necessary testing evidence such
as recordings and or screenshots.

<!-- Generated with the help of the pr-description AI skill -->

Made with [Cursor](https://cursor.com)

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Low risk CI configuration tweak that only affects TestFlight upload
behavior; main risk is unintended cancellation of a prior build that was
still awaiting beta review in the same version train.
> 
> **Overview**
> Updates iOS Fastlane `upload_to_testflight_only` to pass
`reject_build_waiting_for_review: true` to `upload_to_testflight`,
automatically rejecting any prior build stuck *waiting for beta review*
before submitting a new one.
> 
> This prevents CI/TestFlight uploads from failing when Apple allows
only one build per version to be in review at a time, enabling
back-to-back external distribution without manual intervention.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
2af86af. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: tommasini

ios/fastlane/Fastfile

@@ -101,6 +101,7 @@ platform :ios do
     testflight_options = {
       api_key: api_key,
       ipa: ipa_path,
+      reject_build_waiting_for_review: true,
       distribute_external: distribute_external,
       groups: groups,
       notify_external_testers: notify_external_testers,