Bump sphinx from 8.1.0 to 8.1.3

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 8.1.0 to 8.1.3.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/master/CHANGES.rst)
- [Commits](sphinx-doc/sphinx@v8.1.0...v8.1.3)

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

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

pyproject.toml

@@ -25,7 +25,7 @@ Issues = "https://github.com/marshmallow-code/marshmallow-sqlalchemy/issues"
 Source = "https://github.com/marshmallow-code/marshmallow-sqlalchemy"
 
 [project.optional-dependencies]
-docs = ["sphinx==8.1.0", "alabaster==1.0.0", "sphinx-issues==5.0.0"]
+docs = ["sphinx==8.1.3", "alabaster==1.0.0", "sphinx-issues==5.0.0"]
 tests = ["pytest<9", "pytest-lazy-fixtures"]
 dev = ["marshmallow-sqlalchemy[tests]", "tox", "pre-commit>=3.5,<5.0"]