[3.13] gh-91221: fix `test_curses.test_use_default_colors` for xterm-256color (GH-132990) (#132992)

gh-91221: fix `test_curses.test_use_default_colors` for xterm-256color (GH-132990)

Terminals with `xterm-256color` Xterm support may use 15 (bright white) as their default foreground color.
(cherry picked from commit 7f02ded29fb0e7f4ee115b5be32a591ff7b449b8)

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>