feat(tenpayv3): 随官方更新合单下单接口相关模型

src/SKIT.FlurlHttpClient.Wechat.TenpayV3/Models/CombineTransactions/CreateCombineTransactionAppRequest.cs

@@ -97,6 +97,13 @@ namespace SKIT.FlurlHttpClient.Wechat.TenpayV3.Models
                 [Newtonsoft.Json.JsonProperty("settle_info")]
                 [System.Text.Json.Serialization.JsonPropertyName("settle_info")]
                 public Types.Settlement? Settlement { get; set; }
+
+                /// <summary>
+                /// 获取或设置订单优惠标记。
+                /// </summary>
+                [Newtonsoft.Json.JsonProperty("goods_tag")]
+                [System.Text.Json.Serialization.JsonPropertyName("goods_tag")]
+                public string? GoodsTag { get; set; }
             }
 
             public class Payer