CI: Bump actions/download-artifact from 5 to 6

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

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

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

.github/workflows/sop-test-suite.yml

@@ -79,7 +79,7 @@ jobs:
         uses: actions/checkout@v5
       - name: Download test results json artifact
         id: download-test-results
-        uses: actions/download-artifact@v5
+        uses: actions/download-artifact@v6
         with:
           name: test-suite-results.json
       - name: Compare with baseline