auto-rebase: add -f to the filter-branch invocation
...because it tells me to do so:
+ git filter-branch --parent-filter 'sed '\''s/2140bf39/374e6bcc/'\''' --tree-filter 'nix-shell --run treefmt' 374e6bcc..HEAD
Cannot create a new backup.
A previous backup already exists in refs/original/
Force overwriting the backup with -f