fix brew call on linux

.zshrc

@@ -28,4 +28,4 @@ if [ -f '/Users/tom/google-cloud-sdk/path.zsh.inc' ]; then . '/Users/tom/google-
 if [ -f '/Users/tom/google-cloud-sdk/completion.zsh.inc' ]; then . '/Users/tom/google-cloud-sdk/completion.zsh.inc'; fi
 
 
-eval "$(/opt/homebrew/bin/brew shellenv)"
+if [ -f '/opt/homebrew/bin/brew' ]; then eval "$(/opt/homebrew/bin/brew shellenv)"; fi