fix: configure git identity in cleanup workflow

[Arqu]

Summary

• The clean_docs_branch job fails with fatal: empty ident name because no git user.name/user.email is configured on the runner
• Also adds a guard for the "nothing to commit" case (when ≤25 PR dirs exist)

Same fix as n0-computer/iroh#3920

[github-actions]

Documentation for this PR has been generated and is available at: https://n0-computer.github.io/n0-future/pr/25/docs/n0_watcher/

Last updated: 2026-02-09T12:16:17Z