[CI][Docs] install the official requirements

The version we used are old now, which is causing extra warnings.

.github/workflows/gh_pages.yml

@@ -22,7 +22,7 @@ jobs:
     - name: Install deps
       run: |
         sudo apt-get install -y doxygen graphviz ssh ninja-build
-        sudo pip3 install 'sphinx==4.2.0' 'myst-parser==0.15.1' 'recommonmark==0.7.1'
+        sudo pip3 install -r repo/llvm/docs/requirements.txt
     - name: Build Docs
       run: |
         mkdir -p $GITHUB_WORKSPACE/build