Confirming what GP said on version 5.3.1, not seeing any escaping
git checkout <Tab>
git checkout $(./pwd) git checkout <Tab>
git checkout $(./pwd) -% zsh -f
voi% echo $ZSH_VERSION
5.3.1
voi% autoload -U compinit
voi% compinit
voi% git checkout <tab><tab>\$\(./pw3n\)
Already on '$(./pw3n)'
Your branch is up-to-date with 'origin/$(./pw3n)'.
voi% git checkout com<tab>plete_\$\(./foo\)
Switched to branch 'complete_$(./foo)'