set_response_enabled
Description:
Sets whether response is enabled.
If response is not enabled, the corresponding button will have [property@Gtk.Widget:sensitive] set to `FALSE` and it can't be 
      activated as a default response.
response can still be used as [property@MessageDialog:close-response] while it's not enabled.
Responses are enabled by default.
Parameters:
| this | a message dialog | 
| response | a response ID | 
| enabled | whether to enable  |