get_header_suffix
Description:
Gets the suffix for this's header.
Parameters:
| this | 
           a `AdwPreferencesGroup`  | 
      
Returns:
| 
           the suffix for this's header.  | 
      
Gets the suffix for this's header.
| this | 
           a `AdwPreferencesGroup`  | 
      
| 
           the suffix for this's header.  |