Update _test_multiprocessing.py for python#116849

ResourceTracker of a child process should not raise warnings or try to clean up SharedMemory if it was created and is still in use by the parent process. Even if ResourceTracker was asked to track that memory. 
If that was allowed, an error is raised when the parent process tries to unlink the memory later.

Previous commit also makes manual unregistration from resource_tracker unneeded.

Lib/test/_test_multiprocessing.py

@@ -4532,6 +4532,9 @@ def test_shared_memory_tracking(self):
         # gh-82300: When a separate Python process accesses shared memory
         # with track=True, it must cause the memory to be deleted when
         # terminating.
+        # gh-116849: Tracking should only be applied when shared memory
+        # is created, otherwize an error is raised when it is unlinked
+        # in a different process.
         cmd = '''if 1:
             import sys
             from multiprocessing.shared_memory import SharedMemory
@@ -4542,15 +4545,16 @@ def test_shared_memory_tracking(self):
         try:
             rc, out, err = script_helper.assert_python_ok("-c", cmd, mem.name)
             self.assertEqual(rc, 0)
-            self.assertIn(
+            self.assertNotIn(
                 b"resource_tracker: There appear to be 1 leaked "
                 b"shared_memory objects to clean up at shutdown", err)
         finally:
             try:
                 mem.unlink()
-            except OSError:
-                pass
-            resource_tracker.unregister(mem._name, "shared_memory")
+            except OSError as e:
+                self.assertIn(
+                    b"[Errno 2] No such file or directory", str(e)
+                )
             mem.close()
 
 #