chore(deps): bump sphinx from 7.4.7 to 8.1.3 in /docs

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 7.4.7 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@v7.4.7...v8.1.3)

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

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

docs/api/requirements.txt

@@ -3,7 +3,7 @@
 pydata-sphinx-theme==0.15.4
 myst-parser==2.0.0
 # Currently myst-parse is incompatible with sphinx v7
-Sphinx==7.4.7
+Sphinx==8.1.3
 # urllib3 v2.0 only supports OpenSSL 1.1.1+, currently the 'ssl' module is compiled
 # with OpenSSL 1.0.2k-fips  26 Jan 2017.
 # See: https://github.com/urllib3/urllib3/issues/2168,