Bump celery from 4.2.1 to 4.2.2 in /backend/uclapi
Bump celery from 4.2.1 to 4.2.2 in /backend/uclapi

Bumps [celery](https://github.com/celery/celery) from 4.2.1 to 4.2.2.
- [Release notes](https://github.com/celery/celery/releases)
- [Changelog](https://github.com/celery/celery/blob/v4.2.2/Changelog)
- [Commits](https://github.com/celery/celery/compare/v4.2.1...v4.2.2)

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>
uclapi/uclapi,uclapi/uclapi,uclapi/uclapi,uclapi/uclapi