build(deps): bump celery from 5.5.3 to 5.6.0 in /backend

Bumps [celery](https://github.com/celery/celery) from 5.5.3 to 5.6.0.
- [Release notes](https://github.com/celery/celery/releases)
- [Changelog](https://github.com/celery/celery/blob/main/Changelog.rst)
- [Commits](celery/celery@v5.5.3...v5.6.0)

---
updated-dependencies:
- dependency-name: celery
  dependency-version: 5.6.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]