[3.14] gh-79638: Test other HTTP error codes besides 403 in test_robotparser (GH-149569) (GH-149581)

Also, use urllib.request.urlcleanup() in NetworkTestCase.
(cherry picked from commit 57ef2199503387617b8af3d719c74089fb70dbd4)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>