Although a binary (aka ASCII-8BIT) string will never have a broken
coderange, it still has to differentiate between "valid" and "7bit".

On Ruby 3.4/trunk this problem is masked because we now clear the
coderange more agressively in rb_str_resize, and we happened to always
be strinking this string, but we should not assume that.

On Ruby 3.3 this created strings where `ascii_only?` was true in cases
it shouldn't be as well as other problems.

Fixes [Bug #20883]

Co-authored-by: Daniel Colson <danieljamescolson@gmail.com>
Co-authored-by: Matthew Draper <matthew@trebex.net>