Use "python" for markdown code fences in on-hover content (#19082)
Instead of "text".
Closes https://github.com/astral-sh/ty/issues/749
We may not want this because the type display implementations are not
guaranteed to be valid Python, however, unless they're going to
highlight invalid syntax this seems like a better interim value than
"text"? I'm not the expert though. See
https://github.com/astral-sh/ty/issues/749#issuecomment-3026201114 for
prior commentary.
edit: Going back further to
https://github.com/astral-sh/ruff/pull/17057#discussion_r2028151621 for
prior context, it turns out they _do_ highlight invalid syntax in red
which is quite unfortunate and probably a blocker here.
