Bump furo from 2025.9.25 to 2025.12.19 (#692)

Bumps [furo](https://github.com/pradyunsg/furo) from 2025.9.25 to 2025.12.19.
- [Release notes](https://github.com/pradyunsg/furo/releases)
- [Changelog](https://github.com/pradyunsg/furo/blob/main/docs/changelog.md)
- [Commits](pradyunsg/furo@2025.09.25...2025.12.19)

---
updated-dependencies:
- dependency-name: furo
  dependency-version: 2025.12.19
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

pyproject.toml

@@ -30,7 +30,7 @@ Source = "https://github.com/marshmallow-code/marshmallow-sqlalchemy"
 
 [project.optional-dependencies]
 docs = [
-  "furo==2025.9.25",
+  "furo==2025.12.19",
   "sphinx-copybutton==0.5.2",
   "sphinx-design==0.6.1",
   "sphinx-issues==5.0.1",