chore(deps): 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/unit-tests.yml

@@ -229,7 +229,7 @@ jobs:
     steps:
       - uses: actions/checkout@v5
       - name: collect pytest warnings files
-        uses: actions/download-artifact@v5
+        uses: actions/download-artifact@v6
         with:
           pattern: pytest-warnings-json-*
           merge-multiple: true
@@ -288,7 +288,7 @@ jobs:
           python-version: ${{ matrix.python-version }}
 
       - name: Download all artifacts
-        uses: actions/download-artifact@v5
+        uses: actions/download-artifact@v6
         with:
           pattern: coverage-*
           merge-multiple: true