sync might not work with worktree

[gilles]

I get conflicts when syncing after a merge gh stack sync has a warning

⚠ Failed to fast-forward master: failed to run git: fatal: cannot force update the branch 'master' used by worktree at 'XXX'

seems the fix is to git rebase --onto origin/master but gh stack rebase does not have --onto

[loganrosen]

I have a tested fix available on this branch, but repository permissions prevent me from creating a PR. Could a maintainer help me get the necessary access?

[dgenezini]

@skarim , any updates on this? It happens with any command and is a pain when working with worktrees.