fix(review): stub the live-PR verification fetch in the checkbox commit-delivery test

[JSONbored]

Summary

• Main is currently red: test/unit/queue.test.ts's "PR-panel generate-tests checkbox (feat(review): interactive generate-tests checkbox in ORB's PR comment, maintainer-only #4589) > respects the repo's configured commit delivery mode via the checkbox" fails on a clean origin/main checkout, and was already failing at feat(review): interactive generate-tests checkbox in ORB's PR comment, maintainer-only #4600's own merge commit (4d4635709 — validate/validate-code both show conclusion: failure on that commit).
• Root cause: fix(review): verify PR head before E2E test commits #4359 (merged the same day) added a live-PR head/ref/sha re-verification fetch inside commitE2eTestToPrBranch (src/github/e2e-test-commit.ts) before it ever writes a commit, and updated every existing commit-delivery test's fetch stub to handle the new GET /pulls/{n} call. feat(review): interactive generate-tests checkbox in ORB's PR comment, maintainer-only #4600 added this NEW checkbox-specific commit-delivery test without that stub (developed in parallel, unaware of fix(review): verify PR head before E2E test commits #4359), so its fetch mock 404s on the live-PR check and commitE2eTestToPrBranch correctly (fail-safe) declines — zero git-write calls, gitWrites stays [].
• Not a production bug — the actual commit-delivery code path is correct. This is a test-only gap. Adds the exact same GET /pulls/6011 stub the sibling passing tests (commit delivery mode (#4197, #4201) describe block) already use.

Test plan

• npm run typecheck
• npx vitest run test/unit/queue.test.ts -t "respects the repo's configured commit delivery mode via the checkbox" — now passes
• npx vitest run test/unit/queue.test.ts — full file, 783/783 passing

[superagent-security]

Superagent didn't find any vulnerabilities or security issues in this PR.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (main@53bd82b). Learn more about missing BASE report.
⚠️ Report is 4 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

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  Hits            ?    36050           
  Misses          ?     1600           
  Partials        ?      657           

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