Bump paper_trail from 8.1.2 to 9.0.0 in /backend
Bump paper_trail from 8.1.2 to 9.0.0 in /backend

Bumps [paper_trail](https://github.com/airblade/paper_trail) from 8.1.2 to 9.0.0.
- [Release notes](https://github.com/airblade/paper_trail/releases)
- [Changelog](https://github.com/airblade/paper_trail/blob/master/CHANGELOG.md)
- [Commits](https://github.com/airblade/paper_trail/compare/v8.1.2...v9.0.0)

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