fix: remove duplicates from vobj.children

lektor_groupby/backref.py

@@ -49,9 +49,9 @@ class VGroups:
         *,
         fields: Union[str, Iterable[str], None] = None,
         flows: Union[str, Iterable[str], None] = None,
+        order_by: Union[str, Iterable[str], None] = None,
         recursive: bool = True,
         unique: bool = True,
-        order_by: Union[str, Iterable[str], None] = None,
     ) -> Iterator['GroupBySource']:
         ''' Extract all referencing groupby virtual objects from a page. '''
         # prepare filter

lektor_groupby/vobj.py

@@ -46,7 +46,7 @@ class GroupBySource(VirtualSourceObject):
         self.page_num = page_num
 
     def append_child(self, child: 'Record', key_obj: Any) -> None:
-        if child not in self.__children:
+        if child.path not in self.__children:
             self.__children.append(child.path)
         # __key_obj_map is later used to find most used key_obj
         self.__key_obj_map.append(key_obj)