[3.13] gh-117657: Fix TSAN race in free-threaded GC (GH-119883) (#119903)

Only call `gc_restore_tid()` from stop-the-world contexts.
`worklist_pop()` can be called while other threads are running, so use a
relaxed atomic to modify `ob_tid`.
(cherry picked from commit 60593b2052ca275559c11028d50e19f8e5dfee13)

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