publish: Update download-artifact workflow to v4 in publish to PyPi step.

PiperOrigin-RevId: 687015794

Author: naschmitz

.github/workflows/publish.yml

@@ -83,7 +83,7 @@ jobs:
     if: github.event_name == 'release'
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/download-artifact@v2
+      - uses: actions/download-artifact@v4
         with:
           name: releases
           path: dist