Add a test.

Author: serhiy-storchaka

Lib/test/test_inspect/test_inspect.py

@@ -5916,6 +5916,7 @@ def test_sysconfig_module_has_signatures(self):
     def test_threading_module_has_signatures(self):
         import threading
         self._test_module_has_signatures(threading)
+        self.assertIsNotNone(inspect.signature(threading.__excepthook__))
 
     def test_thread_module_has_signatures(self):
         import _thread