**Describe the unexpected behaviour**

Neither of these works:
```
now64(3, 'UTC')
now64('UTC', 3)
```
{
        UInt32 scale = DataTypeDateTime64::default_scale;
        auto res_type = removeNullable(result_type);
        if (const auto * type = typeid_cast<const DataTypeDateTime64 *>(res_type.get()))
            scale = type->getScale();
        return std::make_unique<FunctionBaseNow64>(nowSubsecond(scale), result_type);
    }
};
}
void registerFunctionNow64(FunctionFactory & factory)
{
    factory.registerFunction<Now64OverloadResolver>(FunctionFactory::CaseInsensitive);
}
}