ci: re-enable CI on PRs targeting stable cp-7.76.0 (#29986)

## **Description**

Re-enables the `ci` workflow on pull requests whose base is `stable`
(the release `release/X.Y.Z -> stable` PRs).

PR
[#29305](https://github.com/MetaMask/metamask-mobile/pull/29305/changes#diff-b803fcb7f17ed9235f1e5cb1fcd2f5d3b2838429d4368ae4c57ce4436577f03f)
accidentally added `branches-ignore: stable` in
`.github/workflows/ci.yml`, which makes the workflow refuse to run on
any PR whose base branch is `stable`.

We have branch protection on `stable`, which requires the `Check all
jobs pass` and `All jobs pass` status checks.
So `Check all jobs pass` / `All jobs pass` never appeared (no `ci` run)
on the release PR :
#29584, so the release
PR currently cannot be merged.


## **Changelog**

CHANGELOG entry: null

## **Related issues**

Refs: #29584 (release/7.76.0 PR currently blocked by the missing CI
checks)
Refs: #29305 (introduced the regression)


## **Manual testing steps**

N/A 

## **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.

#### Performance checks (if applicable)

- [x] I've tested on Android
  - Ideally on a mid-range device; emulator is acceptable
- [x] I've tested with a power user scenario
- Use these [power-user
SRPs](https://consensyssoftware.atlassian.net/wiki/spaces/TL1/pages/edit-v2/401401446401?draftShareId=9d77e1e1-4bdc-4be1-9ebb-ccd916988d93)
to import wallets with many accounts and tokens
- [x] I've instrumented key operations with Sentry traces for production
performance metrics
- See [`trace()`](/app/util/trace.ts) for usage and
[`addToken`](/app/components/Views/AddAsset/components/AddCustomToken/AddCustomToken.tsx#L274)
for an example

For performance guidelines and tooling, see the [Performance
Guide](https://consensyssoftware.atlassian.net/wiki/spaces/TL1/pages/400085549067/Performance+Guide+for+Engineers).

## **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 -->

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Low risk: only adjusts GitHub Actions trigger filters so CI runs on
`stable`-based pull requests again, with no production code changes.
> 
> **Overview**
> Re-enables the `ci` GitHub Actions workflow for pull requests
targeting `stable` by removing the `pull_request.branches-ignore:
stable` filter, allowing required CI checks to run on release PRs again.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
6e0ed20. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: chloeYue

.github/workflows/ci.yml

@@ -8,8 +8,6 @@ on:
       - opened
       - reopened
       - synchronize
-    branches-ignore:
-      - stable
   merge_group:
   schedule:
     # Run the full suite "overnight," once every hour from 2:00am UTC until 6:00am UTC.