build(deps): bump actions/download-artifact from 4.1.3 to 8.0.1

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 4.1.3 to 8.0.1.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](https://github.com/actions/download-artifact/compare/v4.1.3...v8.0.1)

---
updated-dependencies:
- dependency-name: actions/download-artifact
  dependency-version: 8.0.1
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

.github/workflows/nightly-artifacts.yml

@@ -494,7 +494,7 @@ jobs:
           echo "FLATPAK_GPG_KEY_ID=$(gpg --list-secret-keys --with-colons | awk -F: '/^fpr/{print $10; exit}')" >> "$GITHUB_ENV"
 
       - name: Download OSTree repo artifact
-        uses: actions/download-artifact@v4.1.3
+        uses: actions/download-artifact@v8.0.1
         with:
           name: flatpak-ostree-repo
           path: flatpak-ostree-repo/