Bump actions/download-artifact from 5 to 6 (#126)

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
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -48,7 +48,7 @@ jobs:
     steps:
     - uses: actions/checkout@v5
 
-    - uses: actions/download-artifact@v5
+    - uses: actions/download-artifact@v6
       with:
         name: testcases