Bump sphinx-substitution-extensions from 2025.12.15 to 2026.1.12

Bumps [sphinx-substitution-extensions](https://github.com/adamtheturtle/sphinx-substitution-extensions) from 2025.12.15 to 2026.1.12.
- [Release notes](https://github.com/adamtheturtle/sphinx-substitution-extensions/releases)
- [Changelog](https://github.com/adamtheturtle/sphinx-substitution-extensions/blob/main/CHANGELOG.rst)
- [Commits](adamtheturtle/sphinx-substitution-extensions@2025.12.15...2026.01.12)

---
updated-dependencies:
- dependency-name: sphinx-substitution-extensions
  dependency-version: 2026.1.12
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

pyproject.toml

@@ -70,7 +70,7 @@ optional-dependencies.dev = [
     "sphinx-copybutton==0.5.2",
     "sphinx-lint==1.0.2",
     "sphinx-pyproject==0.3.0",
-    "sphinx-substitution-extensions==2025.12.15",
+    "sphinx-substitution-extensions==2026.1.12",
     "sphinxcontrib-spelling==8.0.2",
     "sybil==9.3.0",
     "ty==0.0.10",