selftests: harness: Don't set setup_completed for fixtureless tests

This field is unused and has no meaning for tests without fixtures.
Don't set it for them.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Link: https://lore.kernel.org/r/20250505-nolibc-kselftest-harness-v4-8-ee4dd5257135@linutronix.de


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