fix(fish): use absolute brew paths in config.fish

Previously `(brew --prefix)/bin` was being used. This caused a
chicken/egg problem though, because we couldn't call `brew` until it was
in the path. New Macs are Apple Si now, so assuming those paths
(`/opt/homebrew`) is probably an acceptable assumption.

dot_config/private_fish/config.fish

@@ -19,7 +19,7 @@ if status is-interactive
     fish_vi_key_bindings
 
     fish_add_path "$HOME/.cargo/bin"
-    fish_add_path "$(brew --prefix)/bin" "$(brew --prefix)/sbin"
+    fish_add_path /opt/homebrew/bin /opt/homebrew/sbin
 
     alias sr='ssh -l root'