enum_to_string
Description:
[ Version ( replacement = "UpgradeKindEnum.to_string" ,  since = "0.6.11" ) ]
public unowned string enum_to_string ()
  public unowned string enum_to_string ()
Converts a enumerated type to its text representation
Parameters:
| upgrade_kind | 
           The enumerated type value  | 
      
Returns:
| 
           the enumerated constant value, e.g. "minimal"  |