[3.12] gh-123570: Add link to `weakref.ref` from `weakref_slot` docs in `dataclasses` (GH-123571) (#123595)

gh-123570: Add link to `weakref.ref` from `weakref_slot` docs in `dataclasses` (GH-123571)
(cherry picked from commit c3ed775899eedd47d37f8f1840345b108920e400)

Co-authored-by: sobolevn <mail@sobolevn.me>