Make zsh completions tests pass on macOS machines

[PawelLipski]

Tests/things that pass/work:

• bash/fish completion tests on macOS machine on CI
• zsh completion tests on my macbook
• zsh completions for git on macOS machine on CI

Only this specific combination doesn't want to pass (is currently ignored) :/

A place to start might be to check if other completions for git plugins (like git-flow or git-lfs) pass on macOS on CI.

[PawelLipski]

Whoops, zsh completion tests on my macbook no longer pass :trollface: