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/docker.yml

@@ -151,7 +151,7 @@ jobs:
             }
             return out;
 
-      - uses: actions/download-artifact@v5
+      - uses: actions/download-artifact@v6
         with:
           name: ${{ matrix.dist }}-${{ matrix.arch }}-${{ github.run_number }}
           path: docker/coturn/.cache/
@@ -208,7 +208,7 @@ jobs:
                         ||     'edge' }}-${{ matrix.dist }}"
              >> $GITHUB_OUTPUT
 
-      - uses: actions/download-artifact@v5
+      - uses: actions/download-artifact@v6
         with:
           path: docker/coturn/.cache/