fix: update __get_value return type to support broader value types

Author: gabino

mongoengine_plus/types/enum_field.py

@@ -1,5 +1,5 @@
 from enum import Enum
-from typing import Type
+from typing import Any, Type, Union
 
 from mongoengine.base import BaseField
 
@@ -18,8 +18,8 @@ def __init__(self, enum: Type[Enum], *args, **kwargs):
         kwargs['choices'] = [choice for choice in enum]
         super(EnumField, self).__init__(*args, **kwargs)
 
-    def __get_value(self, enum: Enum) -> str:
-        return enum.value
+    def __get_value(self, enum: Enum) -> Union[str, Any]:
+        return enum.value if hasattr(enum, 'value') else enum
 
     def to_python(self, value: Enum) -> Enum:  # pragma: no cover
         return self.enum(super(EnumField, self).to_python(value))