[3.11] gh-91687: modernize dataclass example typing (GH-103773) (#103774)

modernize dataclass example typing `list` rather than `List` and comment
as to that line being the alluded too error.
(cherry picked from commit 7ef614c1adad2b8857442bf0fea649891b591109)

Co-authored-by: Allan Lago <35788148+alago1@users.noreply.github.com>
Co-authored-by: Łukasz Langa <lukasz@langa.pl>