ghcup setup nukes symlinks in fish's config files

Context: setting up ghcup in a Linux environment, using the 'fish' shell. After setup, ghcup replaces the symlink with a standard file.

Setup with:

    curl --proto '=https' --tlsv1.2 -sSf https://get-ghcup.haskell.org | sh

After setup, fish's config file in $HOME/.config/fish/config.fish is a standard file. Before starting ghcup's setup, this file was a symlink.