[3.12] gh-104522: Fix test_subprocess failure when build Python in the root home directory (GH-114236) (GH-114239)

EPERM is raised when setreuid() fails.
EACCES is set in execve() when the test user has not access to sys.executable.
(cherry picked from commit 311d1e2701037952eaf75f993be76f3092c1f01c)

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