Update (ci): github action's artifact upgrade due to EOL for versions less than v4

Author: alleeclark

.github/workflows/docs-build.yml

@@ -20,10 +20,11 @@ jobs:
     steps:
       - uses: actions/checkout@v4 # deploy needs git credentials
       - name: Download prepared docs
-        uses: actions/download-artifact@v3
+        uses: actions/download-artifact@v4
         with:
           name: docs-html-${{ github.sha }}
           path: docs/build/html
+          merge-multiple: true
 
       - name: Deploy 🚀
         uses: JamesIves/github-pages-deploy-action@v4.6.3