bad substitution when trying to use git effort

[xytxytxyt]

on macOS 12.6.7 zsh

% brew install git-extras
...
% git effort

  path                                                                                                                                                                                                 commits    active days

/opt/homebrew/bin/git-effort: line 273:  ${nJobs@P} >= nProcs : bad substitution

% git clone https://github.com/tj/git-extras.git
...
% git checkout $(git describe --tags $(git rev-list --tags --max-count=1))
...
% sudo make install 
...
% source /Users/xian/git-extras/etc/git-extras-completion.zsh
% git effort

  path                                       commits    active days

/usr/local/bin/git-effort: line 273:  ${nJobs@P} >= nProcs : bad substitution

[spacewander]

See #1038