[fix](ci) Use only valid Codex review auth

[shuke987]

What problem does this PR solve?

Issue Number: None

Related PR: None

Problem Summary: The automated code review runner randomly selected auth.json.2, auth.json.3, or auth.json.4. The first two credentials now have revoked refresh tokens and cause reviews to fail with HTTP 401. This change temporarily restricts review runs to the currently valid auth.json.4 credential.

Release note

None

Check List (For Author)

• Test: Manual test
  • Parsed .github/workflows/code-review-runner.yml as YAML
  • Ran git diff --check
• Behavior changed: Yes. Automated code reviews temporarily use only auth.json.4.
• Does this need documentation: No

[hello-stephen]

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