Variable Explorer: Fix error when inserting items in dataframeeditor

- This error was due to a comparison for the item's value that was not
specific enough.
- It started to appear with Numpy 2.2.0, which raises a ValueError for
comparisons with empty arrays.

spyder/plugins/variableexplorer/widgets/dataframeeditor.py

@@ -1143,7 +1143,7 @@ def insert_item(self, axis=0, before_above=False):
                     new_name = self.next_index_name(indexes, new_name)
 
             item_value = eval(eval_type)
-            if item_value == ():
+            if isinstance(item_value, tuple) and item_value == ():
                 item_value = ('')
 
             df.insert(