bpo-37322: Fix test_ssl.test_pha_required_nocert() ResourceWarning (GH-14662)

Close the TLS connection in test_pha_required_nocert() of test_ssl to
fix a ResourceWarning.

Lib/test/test_ssl.py

@@ -2382,6 +2382,7 @@ class ThreadedEchoServer(threading.Thread):
                         if self.server.chatty and support.verbose:
                             sys.stdout.write(err.args[1])
                         # test_pha_required_nocert is expecting this exception
+                        self.close()
                         raise ssl.SSLError('tlsv13 alert certificate required')
                 except OSError:
                     if self.server.chatty: