docs: bump furo from 2024.8.6 to 2025.9.25 in /docs

Bumps [furo](https://github.com/pradyunsg/furo) from 2024.8.6 to 2025.9.25.
- [Release notes](https://github.com/pradyunsg/furo/releases)
- [Changelog](https://github.com/pradyunsg/furo/blob/main/docs/changelog.md)
- [Commits](https://github.com/pradyunsg/furo/compare/2024.08.06...2025.09.25)

---
updated-dependencies:
- dependency-name: furo
  dependency-version: 2025.9.25
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

docs/requirements.txt

@@ -1,2 +1,2 @@
-furo==2024.8.6
+furo==2025.9.25
 sphinx==8.1.3