bpo-44449: faulthandler don't modify frame refcnt (GH-27850)

Fix a crash in the signal handler of the faulthandler module: no
longer modify the reference count of frame objects.
(cherry picked from commit fe997e1a67835a929705c8c305d41c4d7dd326e3)

Co-authored-by: Victor Stinner <vstinner@python.org>