build(deps): update sphinx requirement from ^7.2.6 to ^8.1.3 (#20)

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/v8.1.3/CHANGES.rst)
- [Commits](sphinx-doc/sphinx@v7.2.6...v8.1.3)

---
updated-dependencies:
- dependency-name: sphinx
  dependency-version: 8.1.3
  dependency-type: direct:production
...

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

Author: dependabot[bot]

pyproject.toml

@@ -43,7 +43,7 @@ types-setuptools = "*"
 optional = true
 
 [tool.poetry.group.docs.dependencies]
-sphinx = "^7.2.6"
+sphinx = "^8.1.3"
 sphinx-rtd-theme = "^3.0.2"
 myst-parser = "^4.0.1"
 sphinxcontrib-napoleon = "^0.7"