tests/commonlib/rational-test: Use test group runner wrapper

coreboot unit-tests framework requires tests to use
cb_run_group_tests() instead of cmocka_run_group_tests() for Jenkins
to work correctly. Wrapper ensures that each test has its own report
file and does not overwrite results of other tests.

Signed-off-by: Jakub Czapiga <jacz@semihalf.com>
Change-Id: Iead63cab0465f37b2da0c7b3ef256057e3a191a2
Reviewed-on: https://review.coreboot.org/c/coreboot/+/67371
Reviewed-by: Yu-Ping Wu <yupingso@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

tests/commonlib/rational-test.c

@@ -52,6 +52,6 @@ int main(void)
 		cmocka_unit_test(test_rational),
 	};
 
-	return cmocka_run_group_tests(tests, NULL, NULL);
+	return cb_run_group_tests(tests, NULL, NULL);
 }