build(deps-dev): bump flatted in /serverpackcreator-web-frontend

Bumps [flatted](https://github.com/WebReflection/flatted) from 3.3.3 to 3.4.2.
- [Commits](https://github.com/WebReflection/flatted/compare/v3.3.3...v3.4.2

)

---
updated-dependencies:
- dependency-name: flatted
  dependency-version: 3.4.2
  dependency-type: indirect
...

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