[3.12] gh-110391: socket NetworkConnectionAttributesTest always declare cli (GH-110401) (#110405)

gh-110391: socket NetworkConnectionAttributesTest always declare cli (GH-110401)

NetworkConnectionAttributesTest of test_socket now always declare the
'cli' attribute, so clientTearDown() cannot fail with AttributeError.
(cherry picked from commit e37d4557c3de0476e76ca4b8a1cc8d2566b86c79)

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