kunit: make FAULT_TEST default to n when PANIC_ON_OOPS

As describe in the help string, the user might want to disable these
tests if they don't like to see stacktraces/BUG etc in their kernel log.

However, if they enable PANIC_ON_OOPS, these tests also crash the
machine, which it's safe to assume _almost_ nobody wants.

One might argue that _absolutely_ nobody ever wants their kernel to
crash so this should just be a hard dependency instead of a default.
However, since this is rather special code that's anyway concerned with
deliberately doing "bad" things, the normal rules don't seem to apply,
hence prefer flexibility and allow users to set up a crashing Kconfig if
they so choose.

Link: https://lore.kernel.org/r/20251207-kunit-fault-no-panic-v1-1-2ac932f26864@google.com


Signed-off-by: Brendan Jackman <jackmanb@google.com>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>