Error using fzf.vim in pack/plugins/start with MacVim

### Checklist

- [x] I have fzf 0.54.0 or later
- [x] I have searched through the existing issues

### Output of `:echo system(fzf#exec() .. ' --version')`

zsh: parse error near `)' but fzf --version gives: 0.66.1 (brew)

### OS

- [ ] Linux
- [x] macOS
- [ ] Windows
- [ ] Etc.

### Problem / Steps to reproduce

Installed fzf.vim in .vim/pack/my_plugins/start/fzf.vim

Everything worked pretty well until I did :Marks and then I got an error

Error detected while processing function fzf#vim#marks[5]..111_fzf:
line 18:
E1206: Dictionary required for argument 1

On a hunch, I moved fzf.vim to pack/my_plugins/opt/fzf.vim

And everything works. Had a similar problem with the airline plugin not working when installed in start. So I guess the lesson is, if you use MacVim's pack system for installing, put fzf.vim in opt not start.