make docs optional dependencies compatible with python 3.10

Author: daniel-habermann

pyproject.toml

@@ -49,7 +49,7 @@ all = [
     "myst-nb ~= 1.2",
     "numpydoc ~= 1.8",
     "pydata-sphinx-theme ~= 0.16",
-    "sphinx ~= 8.2",
+    "sphinx ~= 8.1.3",
     "sphinx-polyversion == 1.1",
     "sphinx_design ~= 0.6",
     "sphinxcontrib-bibtex ~= 2.6",
@@ -71,7 +71,7 @@ docs = [
     "myst-nb ~= 1.2",
     "numpydoc ~= 1.8",
     "pydata-sphinx-theme ~= 0.16",
-    "sphinx ~= 8.2",
+    "sphinx ~= 8.1.3",
     "sphinx-polyversion == 1.1",
     "sphinx_design ~= 0.6",
     "sphinxcontrib-bibtex ~= 2.6",