Bump sphinx-substitution-extensions from 2025.4.3 to 2025.6.6

Bumps [sphinx-substitution-extensions](https://github.com/adamtheturtle/sphinx-substitution-extensions) from 2025.4.3 to 2025.6.6.
- [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@2025.04.03...2025.06.06)

---
updated-dependencies:
- dependency-name: sphinx-substitution-extensions
  dependency-version: 2025.6.6
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

pyproject.toml

@@ -91,7 +91,7 @@ optional-dependencies.dev = [
     "sphinx-lint==1.0.0",
     "sphinx-paramlinks==0.6",
     "sphinx-pyproject==0.3.0",
-    "sphinx-substitution-extensions==2025.4.3",
+    "sphinx-substitution-extensions==2025.6.6",
     "sphinx-toolbox==4.0.0",
     "sphinxcontrib-httpdomain==1.8.1",
     "sphinxcontrib-spelling==8.0.1",