Bump deploy-pages action

Signed-off-by: itowlson <ivan.towlson@fermyon.com>

Author: itowlson

.github/workflows/mdbook.yml

@@ -70,4 +70,4 @@ jobs:
     steps:
       - name: Deploy to GitHub Pages
         id: deployment
-        uses: actions/deploy-pages@v2
+        uses: actions/deploy-pages@v4