Bump sidekiq from 5.1.3 to 5.2.1 in /backend
Bump sidekiq from 5.1.3 to 5.2.1 in /backend

Bumps [sidekiq](https://github.com/mperham/sidekiq) from 5.1.3 to 5.2.1.
- [Release notes](https://github.com/mperham/sidekiq/releases)
- [Changelog](https://github.com/mperham/sidekiq/blob/master/Changes.md)
- [Commits](https://github.com/mperham/sidekiq/compare/v5.1.3...v5.2.1)

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