Bump eslint from 8.56.0 to 9.21.0 in /frontend

Bumps [eslint](https://github.com/eslint/eslint) from 8.56.0 to 9.21.0.
- [Release notes](https://github.com/eslint/eslint/releases)
- [Changelog](https://github.com/eslint/eslint/blob/main/CHANGELOG.md)
- [Commits](eslint/eslint@v8.56.0...v9.21.0)

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

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

Author: dependabot[bot]