[3.12] gh-106392: Fix inconsistency in deprecation warnings in datetime module (GH-114761) (#114767)

gh-106392: Fix inconsistency in deprecation warnings in datetime module (GH-114761)
(cherry picked from commit dc4cd2c9ba60e2ee7e534e2f6e93c4c135df23b9)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>