frontend: bump @testing-library/jest-dom in /frontend

Bumps [@testing-library/jest-dom](https://github.com/testing-library/jest-dom) from 5.17.0 to 6.9.1.
- [Release notes](https://github.com/testing-library/jest-dom/releases)
- [Changelog](https://github.com/testing-library/jest-dom/blob/main/CHANGELOG.md)
- [Commits](testing-library/jest-dom@v5.17.0...v6.9.1)

---
updated-dependencies:
- dependency-name: "@testing-library/jest-dom"
  dependency-version: 6.9.1
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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Author: dependabot[bot]