selftests/nolibc: run-tests.sh: enable testing via qemu-user

qemu-user is faster than a full system test.

Link: https://lore.kernel.org/r/20770915-nolibc-run-user-v1-2-3caec61726dc@weissschuh.net


Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>