[3.13] gh-123935: Fix typo in `_get_slots` in `dataclasses.py` (GH-123941) (#123991)

gh-123935: Fix typo in `_get_slots` in `dataclasses.py` (GH-123941)
(cherry picked from commit ac918ccad707ab2d7dbb78a4796a7b8a874f334c)

Co-authored-by: sobolevn <[email protected]>
3 files changed