fix(ci): detach HEAD before claude-code-action on fork PR (#464)
PR #451 (来自 fork aeoform/openless, head ref 也叫 beta) 触发 @claude 时,
claude-code-action 执行 `git fetch origin pull/451/head:beta` 把 PR head
拉到本地 beta 分支,但此时 worktree 正 checkout 在 refs/heads/beta,
git 拒绝 fetch 到已 checkout 的分支:
fatal: refusing to fetch into branch 'refs/heads/beta' checked out at ...
Action failed with error: Command failed: git fetch origin --depth=20 pull/451/head:beta
修复: 在 actions/checkout 后立即 git checkout --detach,释放
refs/heads/<default-branch> 这个本地分支名,让 action 自己 fetch 不撞名.
仅在 fork head ref == base ref name 的 corner case 才会触发问题,
detach 对其他场景无副作用.
失败 run: https://github.com/Open-Less/openless/actions/runs/25978532215
Co-authored-by: baiqing <lbx12309@icloud.com>
