build(deps): bump actions/upload-artifact from 4 to 5

Bumps [actions/upload-artifact](https://github.com/actions/upload-artifact) from 4 to 5.
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](actions/upload-artifact@v4...v5)

---
updated-dependencies:
- dependency-name: actions/upload-artifact
  dependency-version: '5'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/vpp-merge-docs.yml

@@ -220,7 +220,7 @@ jobs:
 
       - name: Upload Documentation Artifacts
         if: always()
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: vpp-merge-docs-${{ env.GERRIT_BRANCH }}-rel-ubuntu2404-x86_64-${{ env.GERRIT_CHANGE_NUMBER }}-${{ env.GERRIT_PATCHSET_NUMBER }}
           path: ${{ env.WORKSPACE }}/build-root/docs/