Update RoundtripToUtf8.cs (#45961)

Author: OoLunar

docs/standard/serialization/system-text-json/snippets/how-to/csharp/RoundtripToUtf8.cs

@@ -22,7 +22,7 @@ public static void Main()
             };
 
             // <Serialize>
-            byte[] jsonUtf8Bytes =JsonSerializer.SerializeToUtf8Bytes(weatherForecast);
+            byte[] jsonUtf8Bytes = JsonSerializer.SerializeToUtf8Bytes(weatherForecast);
             // </Serialize>
 
             Console.WriteLine(Encoding.UTF8.GetString(jsonUtf8Bytes));