Bump pydantic from 2.11.2 to 2.11.3 in /backend

Bumps [pydantic](https://github.com/pydantic/pydantic) from 2.11.2 to 2.11.3.
- [Release notes](https://github.com/pydantic/pydantic/releases)
- [Changelog](https://github.com/pydantic/pydantic/blob/main/HISTORY.md)
- [Commits](pydantic/pydantic@v2.11.2...v2.11.3)

---
updated-dependencies:
- dependency-name: pydantic
  dependency-version: 2.11.3
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]