build(deps): bump pydantic from 2.12.3 to 2.12.4 in /backend

Bumps [pydantic](https://github.com/pydantic/pydantic) from 2.12.3 to 2.12.4.
- [Release notes](https://github.com/pydantic/pydantic/releases)
- [Changelog](https://github.com/pydantic/pydantic/blob/v2.12.4/HISTORY.md)
- [Commits](pydantic/pydantic@v2.12.3...v2.12.4)

---
updated-dependencies:
- dependency-name: pydantic
  dependency-version: 2.12.4
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]