[3.8] gh-108342: Break ref cycle in SSLSocket._create() exc (GH-108344)…

… (#108352)

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 64f9935)

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

Lib/ssl.py

@@ -1048,7 +1048,11 @@ def _create(cls, sock, server_side=False, do_handshake_on_connect=True,
                     self.close()
                 except OSError:
                     pass
-                raise notconn_pre_handshake_data_error
+                try:
+                    raise notconn_pre_handshake_data_error
+                finally:
+                    # Explicitly break the reference cycle.
+                    notconn_pre_handshake_data_error = None
         else:
             connected = True