[3.13] gh-124986: Fix test_no_leaking in test_subprocess on NetBSD and FreeBSD (GH-132476) (GH-132498)

On platforms where the file descriptor limit is larger than FD_SETSIZE
that test was always skipped (FreeBSD) or always failing (NetBSD).
(cherry picked from commit f7b24ffefda839f367b048c06879df6bded128a1)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>