Bump sphinx from 7.2.6 to 8.1.3

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 7.2.6 to 8.1.3.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/v8.1.3/CHANGES.rst)
- [Commits](sphinx-doc/sphinx@v7.2.6...v8.1.3)

---
updated-dependencies:
- dependency-name: sphinx
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

pyproject.toml

@@ -55,7 +55,7 @@ docs = [
     "myst_parser==2.0.0",
     "numpydoc==1.8.0",
     "sphinx-copybutton==0.5.2",
-    "sphinx==7.2.6",
+    "sphinx==8.1.3",
     "sphinx_design==0.5.0",
     "myst-nb==1.0.0",
     "sphinx-book-theme==1.1.0",