Fix failing test.

Author: eiriktsarpalis

src/mcpdotnet/Utils/Json/JsonRpcMessageConverter.cs

@@ -84,7 +84,7 @@ public override void Write(Utf8JsonWriter writer, IJsonRpcMessage value, JsonSer
                 JsonSerializer.Serialize(writer, response, options.GetTypeInfo<JsonRpcResponse>());
                 break;
             case JsonRpcError error:
-                JsonSerializer.Serialize(writer, error, options.GetTypeInfo<JsonRpcResponse>());
+                JsonSerializer.Serialize(writer, error, options.GetTypeInfo<JsonRpcError>());
                 break;
             default:
                 throw new JsonException($"Unknown JSON-RPC message type: {value.GetType()}");