Scenario does not support String values

[markaren]

Marking this as a bug as it is expected behavior that setting string values would work.
I remember I tried to fix this back when boolean was not supported either, but was unable to.

switch (type) {
        case cse::variable_type::real: {
            auto f = generate_modifier<double>(mode, event);
            return cse::scenario::variable_action{
                sim, var, cse::scenario::real_modifier{f}, isInput};
        }
        case cse::variable_type::integer: {
            auto f = generate_modifier<int>(mode, event);
            return cse::scenario::variable_action{
                sim, var, cse::scenario::integer_modifier{f}, isInput};
        }
        case cse::variable_type::boolean: {
            auto f = generate_modifier<bool>(mode, event);
            return cse::scenario::variable_action{
                sim, var, cse::scenario::boolean_modifier{f}, isInput};
        }
        default:
            std::ostringstream oss;
            oss << "No scenario action support for variable type: " << to_text(type);
            throw std::invalid_argument(oss.str());
    }