Support naked expected_failure in tests

[jcivlin]

Adding a missing case in processing of expected_failure with no error code.
Example:

    #[test]
    #[expected_failure]
    fun size_limit_fail() {
        let v = V::empty();
        let i = 0;
        // Limit is currently 1024 * 1024
        let max_len = 1024 * 1024 + 1;

        while (i < max_len) {
            V::push_back(&mut v, i);
            i = i + 1;
        };
    }

This fixes tests:

• size_limit_fail in vector_tests,
• timeout_fail_with_expected_failure in move_unit_test.