[3.10] gh-108342: Break ref cycle in SSLSocket._create() exc (GH-108344) (#108350)

Explicitly break a reference cycle when SSLSocket._create() raises an
exception. Clear the variable storing the exception, since the
exception traceback contains the variables and so creates a reference
cycle.

This test leak was introduced by the test added for the fix of GH-108310.
(cherry picked from commit 64f99350351bc46e016b2286f36ba7cd669b79e3)

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