In KqueueIOManager, close the force-wakeup fd

This small bug was introduced in python-triogh-1551

Fixes python-triogh-1621

Author: njsmith

trio/_core/_io_kqueue.py

@@ -44,6 +44,7 @@ def statistics(self):
 
     def close(self):
         self._kqueue.close()
+        self._force_wakeup.close()
 
     def force_wakeup(self):
         self._force_wakeup.wakeup_thread_and_signal_safe()