Fix sphinx version constraint to resolve nvidia-sphinx-theme CI failure

Co-authored-by: leofang <5534781+leofang@users.noreply.github.com>

Author: Copilot

cuda_python/docs/environment-docs.yml

@@ -13,7 +13,7 @@ dependencies:
   - pydata-sphinx-theme
   - pytest
   - scipy
-  - sphinx <8.2.0
+  - sphinx >=7.1,<9.0
   - sphinx-copybutton
   - myst-nb
   - enum_tools