Bump actions/download-artifact from 5.0.0 to 6.0.0

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 5.0.0 to 6.0.0.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@v5.0.0...v6.0.0)

---
updated-dependencies:
- dependency-name: actions/download-artifact
  dependency-version: 6.0.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/tests.yaml

@@ -78,7 +78,7 @@ jobs:
       - name: Install dependencies
         run: pip install -U -r requirements-coverage.txt
       - name: Download all coverage artifacts
-        uses: actions/download-artifact@v5.0.0
+        uses: actions/download-artifact@v6.0.0
       - name: Combine Linux coverage results
         run: |
           coverage combine coverage-linux*/.coverage