Bump furo

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](pradyunsg/furo@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] <[email protected]>

Author: dependabot[bot]

smithy-docgen-core/src/main/resources/software/amazon/smithy/docgen/core/integrations/sphinx/requirements-furo.txt

@@ -1,2 +1,2 @@
 # These are requirements only needed for the base furo theme
-furo==2024.8.6
+furo==2025.9.25