[3.11] Replace the esoteric term 'datum' when describing dict comprehensions (GH-106119) (#106349)

Replace the esoteric term 'datum' when describing dict comprehensions (GH-106119)
(cherry picked from commit 987b712b4aeeece336eed24fcc87a950a756c3e2)

Co-authored-by: Ned Batchelder <ned@nedbatchelder.com>