Update publish-book.yaml

.github/workflows/publish-book.yaml

@@ -58,7 +58,6 @@ jobs:
         run: |
           pip install -r requirements.txt
           pip install jupyter-book==0.14.0 ghp-import
-          pip install sphynx==5.0
           pip install jupyter_client==7.3.5  # downgrade jupyter-client to fix hangs
 
       - name: Build the book