Pin Sphinx version in docs requirements

Removed redundant Sphinx upgrade from CI workflow and explicitly pinned Sphinx to version 9.0.4 in docs/requirements.txt to ensure consistent documentation builds.

Author: BattlefieldDuck

.github/workflows/sphinx-gh-pages.yml

@@ -49,7 +49,6 @@ jobs:
         run: |
           python -m pip install --upgrade pip
           python -m pip install .
-          python -m pip install -U sphinx
           python -m pip install -r docs/requirements.txt
 
       - name: Sphinx API Documentation Generation

docs/requirements.txt

@@ -1,3 +1,4 @@
+sphinx==9.0.4
 sphinx-rtd-theme==3.0.2
 sphinxcontrib-googleanalytics==0.5
 sphinx-docsearch==0.2.0