fix【【test轨迹中台】轨迹内容页，删除提示The Code field is required.,The Content field is required.,The EnContent field is required】

https://www.tapd.cn/60863849/bugtrace/bugs/view/1160863849001049602

src/SJZY.Track.Application.Contract/Dtos/TrackContents/EditTrackContentInput.cs

@@ -25,17 +25,17 @@ public class EditTrackContentInput
     /// <summary>
     /// 轨迹内容代码
     /// </summary>
-    public string Code { get; set; }
+    public string? Code { get; set; }
 
     /// <summary>
     /// 轨迹内容
     /// </summary>
-    public string Content { get; set; }
+    public string? Content { get; set; }
 
     /// <summary>
     /// 轨迹内容英文
     /// </summary>
-    public string EnContent { get; set; }
+    public string? EnContent { get; set; }
 
     /// <summary>
     /// 轨迹标记id