chore(deps): bump orjson from 3.9.10 to 3.9.15 in /backend (#423)

Bumps [orjson](https://github.com/ijl/orjson) from 3.9.10 to 3.9.15.
- [Release notes](https://github.com/ijl/orjson/releases)
- [Changelog](https://github.com/ijl/orjson/blob/master/CHANGELOG.md)
- [Commits](ijl/orjson@3.9.10...3.9.15)

---
updated-dependencies:
- dependency-name: orjson
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>