chore(deps): bump mongoose from 5.13.23 to 8.19.2 in /backend

Bumps [mongoose](https://github.com/Automattic/mongoose) from 5.13.23 to 8.19.2.
- [Release notes](https://github.com/Automattic/mongoose/releases)
- [Changelog](https://github.com/Automattic/mongoose/blob/master/CHANGELOG.md)
- [Commits](https://github.com/Automattic/mongoose/commits/8.19.2)

---
updated-dependencies:
- dependency-name: mongoose
  dependency-version: 8.19.2
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]