selftests: harness: Detect illegal mixing of kselftest and harness functionality

selftests: harness: Detect illegal mixing of kselftest and harness functionality

Users may accidentally use the kselftest_test_result_*() functions in
their harness tests. If ksft_finished() is not used, the results
reported in this way are silently ignored.

Detect such false-positive cases and fail the test.

A more correct test would be to reject *any* usage of the ksft APIs but
that would force code churn on users.

Correct usages, which do use ksft_finished() will not trigger this
validation as the test will exit before it.

Reported-by: Yuwen Chen <ywen.chen@foxmail.com>
Link: https://lore.kernel.org/lkml/tencent_56D79AF3D23CEFAF882E83A2196EC1F12107@qq.com/
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Link: https://lore.kernel.org/r/20260302-kselftest-harness-v2-4-3143aa41d989@linutronix.de
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>