Update sphinx requirement from ~=7.4 to ~=8.0 (#2494)

* Update sphinx requirement from ~=7.4 to ~=8.0

Updates the requirements on [sphinx](https://github.com/sphinx-doc/sphinx) to permit the latest version.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/v8.0.2/CHANGES.rst)
- [Commits](sphinx-doc/sphinx@v7.4.0...v8.0.2)

---
updated-dependencies:
- dependency-name: sphinx
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

* Upgrade furo too

---------

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Pierre Sassoulas <[email protected]>

Author: dependabot[bot]

doc/requirements.txt

@@ -1,3 +1,3 @@
 -e .
-sphinx~=7.4
-furo==2024.7.18
+sphinx~=8.0
+furo==2024.8.6