gh-156707: Remove the junction created in test_realpath_volume_guid_path()

The junction pointed to a volume without a mount point.  It was left for the
temporary directory cleanup, which descended into it and tried to remove
files on that volume.

os.rmdir() removes the junction itself, not the directory it points to.

Author: serhiy-storchaka

Lib/test/test_ntpath.py

@@ -1585,11 +1585,15 @@ def test_realpath_volume_guid_path(self):
                 except (OSError, subprocess.CalledProcessError):
                     raise unittest.SkipTest('creating the test junction failed')
 
-                for path in 'testjunc', 'testjunc/spam', 'testjunc/spam/eggs':
-                    with self.subTest(path=path):
-                        realpath = ntpath.realpath(path)
-                        self.assertStartsWith(realpath, '\\\\?\\Volume{')
-                        self.assertTrue(ntpath.isabs(realpath), realpath)
+                try:
+                    for path in 'testjunc', 'testjunc/spam', 'testjunc/spam/eggs':
+                        with self.subTest(path=path):
+                            realpath = ntpath.realpath(path)
+                            self.assertStartsWith(realpath, '\\\\?\\Volume{')
+                            self.assertTrue(ntpath.isabs(realpath), realpath)
+                finally:
+                    # Remove the junction, not the volume it points to.
+                    os_helper.rmdir('testjunc')
 
     def test_isfile_invalid_paths(self):
         isfile = ntpath.isfile