Fix typo in error message (#5027)

Author: severo

src/datasets/features/features.py

@@ -1136,7 +1136,7 @@ def get_nested_type(schema: FeatureType) -> pa.DataType:
         )  # however don't sort on struct types since the order matters
     elif isinstance(schema, (list, tuple)):
         if len(schema) != 1:
-            raise ValueError("We defining list feature, you should just provide one example of the inner type")
+            raise ValueError("When defining list feature, you should just provide one example of the inner type")
         value_type = get_nested_type(schema[0])
         return pa.list_(value_type)
     elif isinstance(schema, Sequence):