[3.12] gh-128816: Fix warnings in test_doctest (GH-128817) (GH-128871)

* Fix a deprecation warning for using importlib.resources.abc.ResourceReader.
* Fix an import warning when importing readline (if it has not yet been imported).
(cherry picked from commit 599be687ec7327c30c6469cf743aa4ee9e82232d)

Co-authored-by: Thomas Grainger <tagrain@gmail.com>