Bump billiard from 3.5.0.3 to 3.5.0.4 in /backend/uclapi
Bump billiard from 3.5.0.3 to 3.5.0.4 in /backend/uclapi

Bumps [billiard](https://github.com/celery/billiard) from 3.5.0.3 to 3.5.0.4.
- [Release notes](https://github.com/celery/billiard/releases)
- [Changelog](https://github.com/celery/billiard/blob/master/CHANGES.txt)
- [Commits](https://github.com/celery/billiard/compare/v3.5.0.3...v3.5.0.4)

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