Use 'is not null' instead of '!= null' in Newtonsoft converter to avo…

…id issues if wrapped type implements equality operators

src/Vogen/Templates/AnyOtherType/AnyOtherType_NewtonsoftJsonConverterReferenceType.cs

@@ -15,6 +15,6 @@ public override void WriteJson(Newtonsoft.Json.JsonWriter writer, object value,
             public override object ReadJson(Newtonsoft.Json.JsonReader reader, System.Type objectType, object existingValue, Newtonsoft.Json.JsonSerializer serializer)
             {
                 var result = serializer.Deserialize<VOUNDERLYINGTYPE>(reader);
-                return result != null ? VOTYPE.Deserialize(result) : null;
+                return result is not null ? VOTYPE.Deserialize(result) : null;
             }
         }