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

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

Author: vstinner

Lib/test/test_socket.py

@@ -5356,6 +5356,7 @@ def test_create_connection_timeout(self):
 
 
 class NetworkConnectionAttributesTest(SocketTCPTest, ThreadableTest):
+    cli = None
 
     def __init__(self, methodName='runTest'):
         SocketTCPTest.__init__(self, methodName=methodName)
@@ -5365,7 +5366,8 @@ def clientSetUp(self):
         self.source_port = socket_helper.find_unused_port()
 
     def clientTearDown(self):
-        self.cli.close()
+        if self.cli is not None:
+            self.cli.close()
         self.cli = None
         ThreadableTest.clientTearDown(self)