This doesn't work, git pull fails because of ff-only config in .gitconfig
git pull origin $MAIN_BRANCH:$MAIN_BRANCH --rebase --autostash
git rebase origin/$MAIN_BRANCH --rebase-merges --autostash
can't use git rebase directly from origin
can't use git fetch branch:branch as it doesn't take rebase arg
so the only solution is to stash manually before, as the script does.