bpo-39424: Use assertRaisesRegex instead of assertRaisesRegexp. (GH-18277)

diff --git a/Lib/test/test_signal.py b/Lib/test/test_signal.py
index 5b072b0..45553a6 100644
--- a/Lib/test/test_signal.py
+++ b/Lib/test/test_signal.py
@@ -1289,7 +1289,7 @@
         self.assertEqual(cm.exception.errno, errno.EBADF)
         my_pidfd = os.open(f'/proc/{os.getpid()}', os.O_DIRECTORY)
         self.addCleanup(os.close, my_pidfd)
-        with self.assertRaisesRegexp(TypeError, "^siginfo must be None$"):
+        with self.assertRaisesRegex(TypeError, "^siginfo must be None$"):
             signal.pidfd_send_signal(my_pidfd, signal.SIGINT, object(), 0)
         with self.assertRaises(KeyboardInterrupt):
             signal.pidfd_send_signal(my_pidfd, signal.SIGINT)