Fix code generation by ZLoggerMessage

[tetsuzin]

Fix error when EventName is passed to constructor of ZLoggerMessageAttribute.

before

public partial void EventName(global::Microsoft.Extensions.Logging.ILogger logger, int x, int y)
{
    if (!logger.IsEnabled(LogLevel.Warning)) return;
    logger.Log(
        LogLevel.Warning,
        new EventId(12, EventName), // <-- "EventName" is not string
        new EventNameState(x, y),
        null,
        (state, ex) => state.ToString()
    );
}

after

public partial void EventName(global::Microsoft.Extensions.Logging.ILogger logger, int x, int y)
{
    if (!logger.IsEnabled(LogLevel.Warning)) return;
    logger.Log(
        LogLevel.Warning,
        new EventId(12, "EventName"),
        new EventNameState(x, y),
        null,
        (state, ex) => state.ToString()
    );
}

[neuecc]

thanks!!!