GHA CI: Bump actions/upload-artifact in the github-actions group

Bumps the github-actions group with 1 update: [actions/upload-artifact](https://github.com/actions/upload-artifact).


Updates `actions/upload-artifact` from 5 to 6
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](https://github.com/actions/upload-artifact/compare/v5...v6)

---
updated-dependencies:
- dependency-name: actions/upload-artifact
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: github-actions
...

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

.github/workflows/ci_ubuntu.yaml

@@ -182,7 +182,7 @@ jobs:
             ./linuxdeploy-x86_64.AppImage --appdir qbittorrent --output appimage
 
       - name: Upload build artifacts
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: qBittorrent-CI_Ubuntu-x64_${{ matrix.qbt_gui }}_libtorrent-${{ matrix.libtorrent.version }}_Qt-${{ matrix.qt_version }}
           path: upload