⬆ Bump pydantic from 2.11.10 to 2.12.3 in /backend (#1947)

Bumps [pydantic](https://github.com/pydantic/pydantic) from 2.11.10 to 2.12.3.
- [Release notes](https://github.com/pydantic/pydantic/releases)
- [Changelog](https://github.com/pydantic/pydantic/blob/main/HISTORY.md)
- [Commits](pydantic/pydantic@v2.11.10...v2.12.3)

---
updated-dependencies:
- dependency-name: pydantic
  dependency-version: 2.12.3
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]