update deployment

Author: haesleinhuepf

.github/workflows/book.yml

@@ -32,7 +32,7 @@ jobs:
 
     # Push the book's HTML to github-pages
     - name: GitHub Pages action
-      uses: peaceiris/actions-gh-pages@v3.5.9
+      uses: peaceiris/actions-gh-pages@v4
       with:
         github_token: ${{ secrets.GITHUB_TOKEN }}
         publish_dir: ./docs/_build/html