Prepending fails on zsh with only shell integration enabled

[karrtikr]

Testing #182970

envVarCollection.prepend('PS1', '(.venv) ', {
    applyAtProcessCreation: false,
    applyAtShellIntegration: true,
});

seems to fail on zsh shell:

[karrtikr]

Moving this to August same as the other issue: #191753