Update deploy.yml

Author: tomcm39

.github/workflows/deploy.yml

@@ -33,6 +33,7 @@ jobs:
     steps:
       - name: Ensure _build exists
         run: mkdir -p _build
+        run: mkdir -p _build/html
       - uses: actions/checkout@v4
       - name: Setup Pages
         uses: actions/configure-pages@v3