Discarding staged new file is not working

[Danil Menkin]

Reproduction:

 danil   fix/stash-worktree  ~/offw/rust/gitu  echo "meowmeow" > cat.txt
 danil   fix/stash-worktree ?:1  ~/offw/rust/gitu  gitu -k "jsjKy<enter>"

Yields error:

I think we want to git restore --staged <file> followed by std::fs::remove_file(file), right?