Pin Sphinx <8.2.0 to fix doc build (#456)

* pin Sphinx to fix doc build

* use conda packages only so that conda can apply version constraint correctly

Author: leofang

cuda_python/docs/environment-docs.yml

@@ -10,11 +10,10 @@ dependencies:
   - pydata-sphinx-theme
   - pytest
   - scipy
-  - sphinx
+  - sphinx <8.2.0
   - sphinx-copybutton
-  - pip:
-    - furo
-    - myst-nb
-    - enum-tools
-    - sphinx_toolbox
-    - pyclibrary
+  - furo
+  - myst-nb
+  - enum_tools
+  - sphinx-toolbox
+  - pyclibrary