[FIX] Preprocess: enums containing function names changed

Enums now saved as string and not as int anymore.
https://sentry.io/biolab/orange3/issues/227119437/

Author: jerneju

Orange/preprocess/preprocess.py

@@ -403,8 +403,8 @@ class _MethodEnum(Enum):
         def __call__(self, *args, **kwargs):
             return getattr(Scale, '_' + self.name)(*args, **kwargs)
 
-    CenteringType = _MethodEnum('Scale', 'NoCentering, Mean, Median', type=int)
-    ScalingType = _MethodEnum('Scale', 'NoScaling, Std, Span', type=int)
+    CenteringType = _MethodEnum('Scale', 'NoCentering, Mean, Median')
+    ScalingType = _MethodEnum('Scale', 'NoScaling, Std, Span')
     NoCentering, Mean, Median = CenteringType
     NoScaling, Std, Span = ScalingType