Sphinx 6.2 fix: add nav.contents where that div.topic is used

[hugovk]

Fixes https://github.com/python/python-docs-theme/issues/132 by applying the same fix as https://github.com/sphinx-doc/sphinx/commit/5806f0af2788db40661d62e5e88c2c1560ae46b6.

See https://github.com/python/python-docs-theme/issues/132#issuecomment-1625268649 for details.

Compare:

• Before: https://docs.python.org/3.13/library/asyncio-task.html
• After: https://python-docs-theme-previews--138.org.readthedocs.build/en/138/library/asyncio-task.html

Before	After