build(deps): bump actions/download-artifact from 5 to 6 (#22)

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 5 to 6.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@v5...v6)

---
updated-dependencies:
- dependency-name: actions/download-artifact
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major

[skip ci]
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Author: dependabot[bot]

.github/workflows/nightly.yml

@@ -76,7 +76,7 @@ jobs:
         uses: actions/checkout@v5
 
       - name: Download artifacts
-        uses: actions/download-artifact@v5
+        uses: actions/download-artifact@v6
         with:
           path: artifacts
           merge-multiple: true