Use v3

Author: gmatteo

.github/workflows/build_website.yml

@@ -70,7 +70,7 @@ jobs:
         uses: actions/configure-pages@v4
 
       - name: Upload Pages Artifact
-        uses: actions/upload-pages-artifact@v2
+        uses: actions/upload-pages-artifact@v3
         with:
           path: abinit/site/ # Important. Set to your output dir in MkDocs