Default to color output for ghostty

[chromy]

ghostty is a new terminal, see:

• https://ghostty.org/docs/about
• https://github.com/ghostty-org/ghostty

I did a similar change to the one for alacritty manually listing the string: https://github.com/google/googletest/pull/4490

Although possibly at some point it would become better to do TERM != "xterm-mono" && TERM.startswith("xterm-") or similar rather than manually listing all the terminals.