chore(deps-dev): Bump sphinx-substitution-extensions

Bumps [sphinx-substitution-extensions](https://github.com/adamtheturtle/sphinx-substitution-extensions) from 2026.8.13.1 to 2026.10.9.
- [Release notes](https://github.com/adamtheturtle/sphinx-substitution-extensions/releases)
- [Commits](adamtheturtle/sphinx-substitution-extensions@2026.08.13.1...2026.10.09)

---
updated-dependencies:
- dependency-name: sphinx-substitution-extensions
  dependency-version: 2026.10.9
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

pyproject.toml

@@ -84,7 +84,7 @@ dev = [
     "sphinx-copybutton==0.5.2",
     "sphinx-lint==1.0.2",
     "sphinx-pyproject==0.3.0",
-    "sphinx-substitution-extensions==2026.8.13.1",
+    "sphinx-substitution-extensions==2026.10.9",
     "sphinxcontrib-spelling==8.0.2",
     # ``sphinxcontrib-towncrier`` renders unreleased news fragments
     # as Markdown in docs/source/unreleased.md during Sphinx builds.