[3.12] gh-104341: Call _PyEval_ReleaseLock() with NULL When Finalizing the Current Thread (gh-105109) (gh-105209)

This avoids the problematic race in drop_gil() by skipping the FORCE_SWITCHING code there for finalizing threads.

(The idea for this approach came out of discussions with @markshannon.)
(cherry picked from commit 3698fda)

Co-authored-by: Eric Snow ericsnowcurrently@gmail.com