[DX-4969] Handle merge_group events

[kalverra]

merge_group events had issues with git history, as we didn't fetch the proper git history. The git pull fallback didn't work properly either. Now we fetch proper history with the API.

Tested on smartcontractkit/chainlink#23386

[github-actions]

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[github-actions]

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[Copilot]

Pull request overview

This PR updates the advanced-triggers action to handle merge_group events more reliably by switching to GitHub API-based file change detection (with git-based fallbacks) and improving how missing git refs are fetched when diffs require additional history.

Changes:

• Add merge_group changed-file detection via repos.compareCommits and route it through getChangedFiles(...).
• Replace the prior git pull fallback with a shallow git fetch of missing refs (optionally authenticated).
• Add Vitest coverage for the new routing and helper behavior, plus a changeset for a patch release.

Reviewed changes

Copilot reviewed 7 out of 9 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
pnpm-lock.yaml	Updates lockfile metadata for the workspace.
actions/advanced-triggers/src/run.ts	Routes merge_group changed-file detection through API with git fallback; threads token through git paths.
actions/advanced-triggers/src/github.ts	Adds getChangedFilesForMergeGroup using repos.compareCommits.
actions/advanced-triggers/src/git.ts	Replaces git pull fallback with shallow fetch of missing refs; supports authenticated fetch.
actions/advanced-triggers/src/tests/run.test.ts	Adds routing tests for merge_group and verifies fallback behavior.
actions/advanced-triggers/src/tests/github.test.ts	Adds tests for merge-group file extraction from API responses.
actions/advanced-triggers/src/tests/git.test.ts	Adds tests for shallow-fetch fallback behavior in git diff path.
actions/advanced-triggers/dist/index.js	Updates the bundled action output to match source changes.
.changeset/sweet-horns-bite.md	Declares a patch release for advanced-triggers.

Files not reviewed (1)

• pnpm-lock.yaml: Generated file

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[Copilot]

Pull request overview

Copilot reviewed 7 out of 9 changed files in this pull request and generated no new comments.

Files not reviewed (1)

• pnpm-lock.yaml: Generated file

Suppressed comments (1)

actions/advanced-triggers/src/run.ts:214

• The merge_group changed-file strategy now uses the GitHub API (compareCommits) with a git fallback, but the action documentation still states that merge_group uses git diff --name-only (see actions/advanced-triggers/README.md table under “Supported events”). This mismatch can mislead workflow authors troubleshooting behavior and required permissions.

    case "merge_group": {
      return getChangedFilesForMergeGroupWithFallback(
        octokit,
        owner,
        repo,
        event.base,
        event.head,
        repositoryRoot,
        token,
      );
    }