Bump serverless-offline from 11.2.1 to 13.0.0 in /backend

Bumps [serverless-offline](https://github.com/dherault/serverless-offline) from 11.2.1 to 13.0.0.
- [Release notes](https://github.com/dherault/serverless-offline/releases)
- [Changelog](https://github.com/dherault/serverless-offline/blob/master/CHANGELOG.md)
- [Commits](dherault/serverless-offline@v11.2.1...v13.0.0)

---
updated-dependencies:
- dependency-name: serverless-offline
  dependency-type: direct:development
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>