gh-action: bump actions/upload-artifact from 3 to 4

Bumps [actions/upload-artifact](https://github.com/actions/upload-artifact) from 3 to 4.
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](https://github.com/actions/upload-artifact/compare/v3...v4)

---
updated-dependencies:
- dependency-name: actions/upload-artifact
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/release.yml

@@ -23,7 +23,7 @@ jobs:
           hugo-version: 'latest'
       - name: Build pages
         run: hugo $(cat .hugo-params)
-      - uses: actions/upload-artifact@v3
+      - uses: actions/upload-artifact@v4
         name: Upload pages
         with:
           name: pages
@@ -62,7 +62,7 @@ jobs:
         run: cp static/all.ics public/all.ics
       - name: Update homepage with latest event
         run: upcoming="$(python tools/gen_upcoming.py static/all.ics 20 5 | tr '\n' ' ')" && sed -i "s#CALENDAR#$upcoming#g" public/index.html
-      - uses: actions/upload-artifact@v3
+      - uses: actions/upload-artifact@v4
         name: Upload pages
         with:
           name: enhanced_pages