Reintroduce set for JsonParsingException.ActualChar (#5090) (#5320)

(cherry picked from commit 5f937c1)

Author: stevejgordon

src/Elasticsearch.Net/Utf8Json/JsonReader.cs

@@ -1168,7 +1168,7 @@ public class JsonParsingException : Exception
 		private readonly WeakReference _underlyingBytes;
 		private readonly int _limit;
         public int Offset { get; }
-        public string ActualChar { get; }
+        public string ActualChar { get; set; }
 
         public JsonParsingException(string message)
             : base(message)