kasan: don't run tests in async mode

Asynchronous KASAN mode doesn't guarantee that a tag fault will be
detected immediately and causes tests to fail. Forbid running them
in asynchronous mode.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>