Update build_docs.yml

switch to actions/download-artifact v4

Author: MarAlder

.github/workflows/build_docs.yml

@@ -74,7 +74,7 @@ jobs:
       - name: Setup Pages
         uses: actions/configure-pages@v3
       - name: Download html zip
-        uses: actions/download-artifact@v3
+        uses: actions/download-artifact@v4
         with:
           name: cpacsDocs
       - name: Extract HTML Docs