Bump flatted and eslint in /frontend

Bumps [flatted](https://github.com/WebReflection/flatted) to 3.4.2 and updates ancestor dependency [eslint](https://github.com/eslint/eslint). These dependencies need to be updated together.


Updates `flatted` from 2.0.1 to 3.4.2
- [Commits](WebReflection/flatted@v2.0.1...v3.4.2)

Updates `eslint` from 6.8.0 to 10.1.0
- [Release notes](https://github.com/eslint/eslint/releases)
- [Commits](eslint/eslint@v6.8.0...v10.1.0)

---
updated-dependencies:
- dependency-name: flatted
  dependency-version: 3.4.2
  dependency-type: indirect
- dependency-name: eslint
  dependency-version: 10.1.0
  dependency-type: direct:development
...

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Author: dependabot[bot]