Update actions/upload-artifact action to v6

| datasource  | package                 | from | to |
| ----------- | ----------------------- | ---- | -- |
| github-tags | actions/upload-artifact | v4   | v6 |


Signed-off-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/ci.yaml

@@ -102,7 +102,7 @@ jobs:
 
       - name: Upload digests (main only)
         if: ${{ github.ref_name == 'main' }}
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v6
         with:
           name: digests-${{ matrix.version }}-${{ matrix.platform.id }}
           path: /tmp/digests/${{ matrix.version }}-${{ matrix.platform.id }}.txt