[3.14] gh-139774: use relaxed atomics for datetime hashes (GH-139775) (#139780)

gh-139774: use relaxed atomics for datetime hashes (GH-139775)
(cherry picked from commit 49fb46f555881c9f2d20ca87c8187c8718217c77)

Co-authored-by: Kumar Aditya <kumaraditya@python.org>