[BUG] Base zshrc should only eval `brew` if it exists

[TechDufus]

Is there an existing issue for this?

• [X] I have searched the existing issues

Current Behavior

Getting error on new install as of b898b3c:

/home/user/.zshrc:6: no such file or directory: /opt/homebrew/bin/brew

Expected Behavior

This should only eval if the file opt/homebrew/bin/brew exists.

Steps To Reproduce

No response

Environment

• OS: Ubuntu 22LTS

Anything else?

No response