test: adds missing var on android repacked builds (MetaMask#24328)

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## **Description**
Adds a missing var on repack Android builds. This hasn't been an issue
on iOS since the iOS build workflow sets the env on an upper level where
this var is present.

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## **Related issues**

Fixes:

## **Manual testing steps**

```gherkin
Feature: my feature name

  Scenario: user [verb for user action]
    Given [describe expected initial app state]

    When user [verb for user action]
    Then [describe expected outcome]
```

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### **After**

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## **Pre-merge author checklist**

- [ ] I’ve followed [MetaMask Contributor
Docs](https://github.com/MetaMask/contributor-docs) and [MetaMask Mobile
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Standards](https://github.com/MetaMask/metamask-mobile/blob/main/.github/guidelines/CODING_GUIDELINES.md).
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- [ ] I've manually tested the PR (e.g. pull and build branch, run the
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as recordings and or screenshots.

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Enables pooled staking in Android E2E artifacts by setting the
required env flag during both build and repack.
> 
> - Adds `MM_POOLED_STAKING_ENABLED: 'true'` to the env of `Build
Android E2E APKs` and `Repack APK with JS updates` in
`.github/workflows/build-android-e2e.yml`
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
2373562. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: christopherferreira9

.github/workflows/build-android-e2e.yml

@@ -201,6 +201,7 @@ jobs:
           SEEDLESS_ONBOARDING_ENABLED: 'true'
           MM_NOTIFICATIONS_UI_ENABLED: 'true'
           MM_SECURITY_ALERTS_API_ENABLED: 'true'
+          MM_POOLED_STAKING_ENABLED: 'true'
           FEATURES_ANNOUNCEMENTS_ACCESS_TOKEN: ${{ secrets.FEATURES_ANNOUNCEMENTS_ACCESS_TOKEN }}
           FEATURES_ANNOUNCEMENTS_SPACE_ID: ${{ secrets.FEATURES_ANNOUNCEMENTS_SPACE_ID }}
           SEGMENT_WRITE_KEY_QA: ${{ secrets.SEGMENT_WRITE_KEY_QA }}