Bump json_matchers from 0.7.3 to 0.9.0 in /backend
Bump json_matchers from 0.7.3 to 0.9.0 in /backend

Bumps [json_matchers](https://github.com/thoughtbot/json_matchers) from 0.7.3 to 0.9.0.
- [Release notes](https://github.com/thoughtbot/json_matchers/releases)
- [Changelog](https://github.com/thoughtbot/json_matchers/blob/master/NEWS.md)
- [Commits](https://github.com/thoughtbot/json_matchers/compare/v0.7.3...v0.9.0)

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