Ignore PendingDeprecationWarning about parser_name deprecation with Docutils 0.22

[mitya57]

Otherwise, with the latest Sphinx and Docutils releases (8.2.3 and 0.22.3), the tests fail with:

  File "/home/dmitry/.virtualenvs/sphinx-book-theme/lib/python3.13/site-packages/sphinx/builders/html/__init__.py", line 154, in __init__
    reader: Reader[DocTreeInput] = docutils.readers.doctree.Reader(
                                   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
        parser_name='restructuredtext'
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File "/home/dmitry/.virtualenvs/sphinx-book-theme/lib/python3.13/site-packages/docutils/readers/__init__.py", line 70, in __init__
    warnings.warn('Argument "parser_name" will be removed '
    ~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                  'in Docutils 2.0.\n'
                  ^^^^^^^^^^^^^^^^^^^^
                  '  Specify parser name in the "parser" argument.',
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                  PendingDeprecationWarning, stacklevel=2)
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
PendingDeprecationWarning: Argument "parser_name" will be removed in Docutils 2.0.
  Specify parser name in the "parser" argument.

The bad code is in Sphinx so we have no control over it. It seems to be fixed in sphinx-doc/sphinx@c384ab9, but that commit is not a part of any stable release yet.

Downstream Debian bug about failing tests: https://bugs.debian.org/1120185.

[mitya57]

The CI failure with Python 3.14 that is seen here is unrelated to my changes. pradyunsg/sphinx-theme-builder#51 should fix it.