Update dependency sphinx to v9

Author: renovate[bot]

pyproject.toml

@@ -17,7 +17,7 @@ pre-commit = "^4.5.1"
 [tool.poetry.group.docs.dependencies]
 furo = "^2025.12.19"
 recommonmark = "^0.7.1"
-sphinx = "^8.2.3"
+sphinx = "^9.1.0"
 sphinx-copybutton = "^0.5.2"
 sphinx-design = "^0.7.0"
 sphinxcontrib-apidoc = "^0.6.0"