gh-155732: Join the terminated process in test_repr_lock (GH-155734)

The process was terminated, but not joined, so it was still reported as
a dangling process.

Author: serhiy-storchaka

Lib/test/_test_multiprocessing.py

@@ -1595,6 +1595,7 @@ def test_repr_lock(self):
         event.wait()
         self.assertEqual(f'<Lock(owner=SomeOtherProcess)>', repr(lock))
         p.terminate()
+        p.join()
 
     def test_lock(self):
         lock = self.Lock()