⬆️ Update actions/download-artifact action to v6

Author: renovate[bot]

.github/workflows/tests.yaml

@@ -54,7 +54,7 @@ jobs:
         with:
           fetch-depth: 0
       - name: ⬇️ Download coverage data
-        uses: actions/download-artifact@v5.0.0
+        uses: actions/download-artifact@v6.0.0
       - name: 🏗 Set up Poetry
         run: pipx install poetry
       - name: 🏗 Set up Python ${{ env.DEFAULT_PYTHON }}