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>

lib/test_kasan.c

@@ -51,6 +51,10 @@ static int kasan_test_init(struct kunit *test)
 		kunit_err(test, "can't run KASAN tests with KASAN disabled");
 		return -1;
 	}
+	if (kasan_flag_async) {
+		kunit_err(test, "can't run KASAN tests in async mode");
+		return -1;
+	}
 
 	multishot = kasan_save_enable_multi_shot();
 	hw_set_tagging_report_once(false);