wrong binding for SetTraceLogCallback

[xtofs]

SetTraceLogCallback is declared as

   [DllImport("raylib", CallingConvention = CallingConvention.Cdecl, ExactSpelling = true)]
    public unsafe static extern void SetTraceLogCallback(delegate* unmanaged[Cdecl]<int, sbyte*, sbyte*, void> callback);

but the callback in C is

void CustomLog(int msgType, const char *text, va_list args)

So the last argument of the callback should be va_list, not sbyte*.