Suppress pytest.PytestUnraisableExceptionWarning raised in test cleanup

This patch suppresses UnraisableException warnings that are
occasionally raised when using Python 3.13.

pytest.ini

@@ -69,6 +69,11 @@ filterwarnings =
   ignore:unclosed <socket.socket fd=:ResourceWarning
   ignore:unclosed <ssl.SSLSocket fd=:ResourceWarning
 
+  # FIXME: Python 3.13 no longer ignores IOBase errors raised by the close(),
+  # FIXME: which exposed a possible race condition in test_conn test cleanup.
+  # Ref: https://github.com/cherrypy/cheroot/issues/734
+  ignore:Exception ignored in. <function IOBase.__del__:pytest.PytestUnraisableExceptionWarning
+
 junit_duration_report = call
 junit_family = xunit2
 junit_suite_name = cheroot_test_suite