fix list sorting to replace without indexof (#489)

Co-authored-by: Markus Hütter <huetter@outlook.com>

src/DynamicData/Binding/SortedObservableCollectionAdaptor.cs

@@ -114,7 +114,7 @@ private static void DoUpdate(ISortedChangeSet<TObject, TKey> updates, IObservabl
                         }
                         else
                         {
-                            list.Replace(update.Previous.Value, update.Current);
+                            list[update.CurrentIndex] = update.Current;
                         }
 
                         break;