DOC: Mark pytest module

[xuhdev]

Pytest document currently does not index the top-level package name
pytest, which causes some trouble when building documentation that
cross-refers to the pytest package via :mod:`pytest` .

Reference: https://www.sphinx-doc.org/en/master/usage/restructuredtext/domains.html#role-py-mod

[nicoddemus]

Reference for py:module:: https://www.sphinx-doc.org/en/master/usage/restructuredtext/domains.html#directive-py-module.

[nicoddemus]

Thanks a lot @xuhdev!

[nicoddemus]

Backport: #8224

[QuLogic]

It seems like this added an extra pytest in the intersphinx for marks:

python3 -m sphinx.ext.intersphinx https://pytest.org/en/latest/objects.inv | rg -e '^py' -e '\.mark\.'
py:attribute
py:class
py:exception
py:function
	pytest.pytest.mark.filterwarnings        reference.html#pytest.pytest.mark.filterwarnings
	pytest.pytest.mark.skip                  reference.html#pytest.pytest.mark.skip
	pytest.pytest.mark.skipif                reference.html#pytest.pytest.mark.skipif
	pytest.pytest.mark.usefixtures           reference.html#pytest.pytest.mark.usefixtures
	pytest.pytest.mark.xfail                 reference.html#pytest.pytest.mark.xfail
py:method
py:module
	@pytest.mark.parametrize                 @pytest.mark.parametrize: parametrizing test functions: parametrize.html#pytest-mark-parametrize
	filterwarnings                           @pytest.mark.filterwarnings             : warnings.html#filterwarnings
	parametrizemark                          @pytest.mark.parametrize: parametrizing test functions: parametrize.html#parametrizemark
	pytest.mark.filterwarnings ref           pytest.mark.filterwarnings              : reference.html#pytest-mark-filterwarnings-ref
	pytest.mark.parametrize ref              pytest.mark.parametrize                 : reference.html#pytest-mark-parametrize-ref
	pytest.mark.skip ref                     pytest.mark.skip                        : reference.html#pytest-mark-skip-ref
	pytest.mark.skipif ref                   pytest.mark.skipif                      : reference.html#pytest-mark-skipif-ref
	pytest.mark.usefixtures ref              pytest.mark.usefixtures                 : reference.html#pytest-mark-usefixtures-ref
	pytest.mark.xfail ref                    pytest.mark.xfail                       : reference.html#pytest-mark-xfail-ref

whereas previously, a singular pytest was there:

python3 -m sphinx.ext.intersphinx https://pytest.org/en/4.6.x/objects.inv | rg -e '^py' -e '\.mark\.'
py:attribute
	_pytest.mark.MarkDecorator.args          reference.html#_pytest.mark.MarkDecorator.args
	_pytest.mark.MarkDecorator.kwargs        reference.html#_pytest.mark.MarkDecorator.kwargs
	_pytest.mark.MarkDecorator.name          reference.html#_pytest.mark.MarkDecorator.name
	_pytest.mark.structures.Mark.args        reference.html#_pytest.mark.structures.Mark.args
	_pytest.mark.structures.Mark.kwargs      reference.html#_pytest.mark.structures.Mark.kwargs
	_pytest.mark.structures.Mark.name        reference.html#_pytest.mark.structures.Mark.name
py:class
	_pytest.mark.MarkDecorator               reference.html#_pytest.mark.MarkDecorator
	_pytest.mark.MarkGenerator               reference.html#_pytest.mark.MarkGenerator
	_pytest.mark.structures.Mark             reference.html#_pytest.mark.structures.Mark
py:exception
py:function
	pytest.mark.filterwarnings               reference.html#pytest.mark.filterwarnings
	pytest.mark.skip                         reference.html#pytest.mark.skip
	pytest.mark.skipif                       reference.html#pytest.mark.skipif
	pytest.mark.usefixtures                  reference.html#pytest.mark.usefixtures
	pytest.mark.xfail                        reference.html#pytest.mark.xfail
py:method
	_pytest.mark.MarkDecorator.with_args     reference.html#_pytest.mark.MarkDecorator.with_args
	_pytest.mark.structures.Mark.combined_with reference.html#_pytest.mark.structures.Mark.combined_with
	@pytest.mark.parametrize                 @pytest.mark.parametrize: parametrizing test functions: parametrize.html#pytest-mark-parametrize
	filterwarnings                           @pytest.mark.filterwarnings             : warnings.html#filterwarnings
	parametrizemark                          @pytest.mark.parametrize: parametrizing test functions: parametrize.html#parametrizemark
	pytest.mark.filterwarnings ref           pytest.mark.filterwarnings              : reference.html#pytest-mark-filterwarnings-ref
	pytest.mark.parametrize ref              pytest.mark.parametrize                 : reference.html#pytest-mark-parametrize-ref
	pytest.mark.skip ref                     pytest.mark.skip                        : reference.html#pytest-mark-skip-ref
	pytest.mark.skipif ref                   pytest.mark.skipif                      : reference.html#pytest-mark-skipif-ref
	pytest.mark.usefixtures ref              pytest.mark.usefixtures                 : reference.html#pytest-mark-usefixtures-ref
	pytest.mark.xfail ref                    pytest.mark.xfail                       : reference.html#pytest-mark-xfail-ref

[xuhdev]

@QuLogic Thanks for the catch. #8280 should have fixed the issue.