Bump sphinx, furo, blacken-docs dependencies (#2160)

* Bump the python-packages group with 3 updates

Bumps the python-packages group with 3 updates: [sphinx](https://github.com/sphinx-doc/sphinx), [furo](https://github.com/pradyunsg/furo) and [blacken-docs](https://github.com/asottile/blacken-docs).


Updates `sphinx` from 7.1.2 to 7.2.4
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/master/CHANGES)
- [Commits](https://github.com/sphinx-doc/sphinx/compare/v7.1.2...v7.2.4)

Updates `furo` from 2023.7.26 to 2023.8.19
- [Release notes](https://github.com/pradyunsg/furo/releases)
- [Changelog](https://github.com/pradyunsg/furo/blob/main/docs/changelog.md)
- [Commits](https://github.com/pradyunsg/furo/compare/2023.07.26...2023.08.19)

Updates `blacken-docs` from 1.15.0 to 1.16.0
- [Changelog](https://github.com/adamchainz/blacken-docs/blob/main/CHANGELOG.rst)
- [Commits](https://github.com/asottile/blacken-docs/compare/1.15.0...1.16.0)

---
updated-dependencies:
- dependency-name: sphinx
  dependency-type: direct:development
  update-type: version-update:semver-minor
  dependency-group: python-packages
- dependency-name: furo
  dependency-type: direct:development
  update-type: version-update:semver-minor
  dependency-group: python-packages
- dependency-name: blacken-docs
  dependency-type: direct:development
  update-type: version-update:semver-minor
  dependency-group: python-packages
...

Signed-off-by: dependabot[bot] <support@github.com>

---------

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: Simon Willison <swillison@gmail.com>

.github/workflows/spellcheck.yml

@@ -13,7 +13,7 @@ jobs:
     - name: Set up Python ${{ matrix.python-version }}
       uses: actions/setup-python@v2
       with:
-        python-version: 3.9
+        python-version: 3.11
     - uses: actions/cache@v2
       name: Configure pip caching
       with: