Correct C# syntax in _validate_property example for the Object class

(cherry picked from commit e40b23c619bacf92d3ebd2ea5cf5d49508947cb2)

doc/classes/Object.xml

@@ -314,7 +314,7 @@
 				    {
 				        if (property["name"].AsStringName() == PropertyName.Number && IsNumberEditable)
 				        {
-				            var usage = property["usage"].As>PropertyUsageFlags<() | PropertyUsageFlags.ReadOnly;
+				            var usage = property["usage"].As<PropertyUsageFlags>() | PropertyUsageFlags.ReadOnly;
 				            property["usage"] = (int)usage;
 				        }
 				    }