chore(deps-dev): bump vitest from 1.6.1 to 4.1.9 in /backend

Bumps [vitest](https://github.com/vitest-dev/vitest/tree/HEAD/packages/vitest) from 1.6.1 to 4.1.9.
- [Release notes](https://github.com/vitest-dev/vitest/releases)
- [Changelog](https://github.com/vitest-dev/vitest/blob/main/docs/releases.md)
- [Commits](https://github.com/vitest-dev/vitest/commits/v4.1.9/packages/vitest)

---
updated-dependencies:
- dependency-name: vitest
  dependency-version: 4.1.7
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]