These cases would have missed GitPython's flag ordering and a non-fast-forward worktree merge.

Git refuses to force-move a branch checked out in a linked worktree, which aborted the whole gitup run. Detect those checkouts, merge --ff-only there, and skip remaining git errors so other branches still update.

git branch --force cannot move a worktree-checked-out ref, so these tests lock in that gitup must not abort the run and should fast-forward the worktree instead.