try to fix GitHub Actions build

This is not upload-artifact but upload-pages-artifact,
of which 3 (not 4) is the newest version.

Author: das-g

.github/workflows/deploy.yml

@@ -27,7 +27,7 @@ jobs:
           npm install
           npx honkit build
       - name: Upload artifact
-        uses: actions/upload-pages-artifact@v4
+        uses: actions/upload-pages-artifact@v3
         with:
           path: _book