Update deploy.yml

Author: jedwin3210

.github/workflows/deploy.yml

@@ -37,7 +37,8 @@ jobs:
         timeout-minutes: 15
         run: |
           set -e
-          jupyter book build .
+          jupyter book build --html
+          test -d ./_build/html
 
       - name: Upload artifact
         uses: actions/upload-pages-artifact@v3