Fix Timestamp has string type 🐛

Author: KoditkarVedant

Src/Notion.Client/Api/Search/Parameters/SearchSort.cs

@@ -8,7 +8,6 @@ public class SearchSort
     {
         public SearchDirection Direction { get; set; }
 
-        [JsonConverter(typeof(IsoDateTimeConverter))]
-        public DateTime Timestamp { get; set; }
+        public string Timestamp { get; set; }
     }
 }