feat: bumped sphinx version manually to 8.1.3

Author: moe-ad

requirements/requirements_docs.txt

@@ -8,7 +8,7 @@ nbsphinx==0.9.5
 pypandoc==1.14
 pytest-sphinx==0.6.3
 pyvista==0.44.2
-sphinx==7.1.0
+sphinx==8.1.3
 sphinx-copybutton==0.5.2
 sphinx-gallery==0.18.0
 sphinx-notfound-page==1.0.4