ci: repin fast-forward so the bot replies in English

[AprilNEA]

The fast-forward bot replied in Chinese on #243. Upstream arcboxlabs/actions
now emits English for everything a human sees — PR replies, step summaries, log
lines, job and step names — so this just moves the pin.

arcboxlabs/actions@086869f → @d4cfe77. One line changed; no behaviour change.

[greptile-apps]

Greptile Summary

This PR updates the reusable fast-forward workflow to an English-output revision.

• Replaces the pinned arcboxlabs/actions commit SHA.
• Keeps the existing trigger, permissions, and GitHub App secrets.

Confidence Score: 5/5

The pin is mergeable once the upstream interface and App-token behavior are confirmed unchanged.

The local workflow remains syntactically unchanged apart from the commit SHA.

Compatibility and credential behavior depend on the contents of the newly pinned external revision.

T-Rex Logs

What T-Rex did

• The contract runs were executed and both exited with code 0, differing at the expected SHA pin.
• The focused commit diff shows .github/workflows/fast-forward.yml as the sole changed file and the uses pin as the sole changed line.
• Raw GitHub retrieval succeeded for both immutable revisions, proving that both upstream workflow objects resolve.

_{Ran code and verified through T-Rex}

Important Files Changed

Filename	Overview
.github/workflows/fast-forward.yml	Repins the external reusable workflow while leaving its local caller contract and credentials unchanged.

_{Reviews (1): Last reviewed commit: "ci: repin fast-forward so the bot replie..." | Re-trigger Greptile}

[linear-code]

RUN-51