[TASK] Update GitHub artifact actions

| datasource  | package                   | from | to |
| ----------- | ------------------------- | ---- | -- |
| github-tags | actions/download-artifact | v7   | v8 |
| github-tags | actions/upload-artifact   | v6   | v7 |

Author: renovate[bot]

.github/workflows/tests.yaml

@@ -88,7 +88,7 @@ jobs:
         working-directory: .Build/coverage
         run: sed -i 's#/home/runner/work/mailqueue/mailqueue#${{ github.workspace }}#g' clover.xml
       - name: Upload coverage artifact
-        uses: actions/upload-artifact@v6
+        uses: actions/upload-artifact@v7
         with:
           name: coverage
           path: .Build/coverage/clover.xml
@@ -106,7 +106,7 @@ jobs:
       # Download artifact
       - name: Download coverage artifact
         id: download
-        uses: actions/download-artifact@v7
+        uses: actions/download-artifact@v8
         with:
           name: coverage