[3.13] gh-117657: Fix TSan race in _PyDict_CheckConsistency (GH-121551) (#121590)

The only remaining race in dictobject.c was in _PyDict_CheckConsistency
when the dictionary has shared keys.
(cherry picked from commit 3ec719fabf936ea7a012a76445b860759155de86)

Co-authored-by: Sam Gross <colesbury@gmail.com>