build(deps-dev): bump mypy from 1.18.2 to 1.19.0 in /backend

Bumps [mypy](https://github.com/python/mypy) from 1.18.2 to 1.19.0.
- [Changelog](https://github.com/python/mypy/blob/master/CHANGELOG.md)
- [Commits](python/mypy@v1.18.2...v1.19.0)

---
updated-dependencies:
- dependency-name: mypy
  dependency-version: 1.19.0
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]