Fix deadlock on shutdown if test_current_{exception,frames} fails (#102019)

* Don't deadlock on shutdown if test_current_{exception,frames} fails

These tests spawn a thread that waits on a threading.Event. If the test fails any of its assertions, the Event won't be signaled and the thread will wait indefinitely, causing a deadlock when threading._shutdown() tries to join all outstanding threads.

Co-authored-by: Brett Simmers <bsimmers@meta.com>

* Add a news entry

* Fix whitespace

---------

Co-authored-by: Brett Simmers <bsimmers@meta.com>
Co-authored-by: Oleg Iarygin <oleg@arhadthedev.net>