[api] Bump pydantic from 2.11.3 to 2.11.4 in /backend

Bumps [pydantic](https://github.com/pydantic/pydantic) from 2.11.3 to 2.11.4.
- [Release notes](https://github.com/pydantic/pydantic/releases)
- [Changelog](https://github.com/pydantic/pydantic/blob/main/HISTORY.md)
- [Commits](pydantic/pydantic@v2.11.3...v2.11.4)

---
updated-dependencies:
- dependency-name: pydantic
  dependency-version: 2.11.4
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]