Bump bandit from 1.8.6 to 1.9.3 in /backend (#2047)

Bumps [bandit](https://github.com/PyCQA/bandit) from 1.8.6 to 1.9.3.
- [Release notes](https://github.com/PyCQA/bandit/releases)
- [Commits](PyCQA/bandit@1.8.6...1.9.3)

---
updated-dependencies:
- dependency-name: bandit
  dependency-version: 1.9.3
  dependency-type: direct:development
  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]