bpo-46879: Fix incorrect sphinx object names in doc (GH-31615)

API members documented in sphinx have an object name, which allow the
documentation to be linked from other projects. Sphinx calculates the
object name by prefixing the current module name to the directive
argument, e.g:

.. module:: foo
.. function:: bar.baz

becomes foo.bar.baz. Since these anchors aren't displayed in the
documentation, some mistakes have crept in, namely the Python stdlib
documentation currently contains the objects:

* asyncio.asyncio.subprocess.DEVNULL
* asyncio.asyncio.subprocess.PIPE
* asyncio.asyncio.subprocess.STDOUT
* asyncio.asyncio.subprocess.Process
* multiprocessing.sharedctypes.multiprocessing.Manager
* xml.etree.ElementTree.xml.etree.ElementInclude

This commit fixes this by making use of the :module: option which
without an argument makes sphinx take the directive argument as is
for the object name (avoiding the prefixing of the current module
name that led to these broken object names).

Co-authored-by: Łukasz Langa <lukasz@langa.pl>