Bump flatted and stylelint in /public/plugins/coreui-icons

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


Updates `flatted` from 2.0.2 to 3.4.2
- [Commits](WebReflection/flatted@v2.0.2...v3.4.2)

Updates `stylelint` from 13.5.0 to 13.13.1
- [Release notes](https://github.com/stylelint/stylelint/releases)
- [Changelog](https://github.com/stylelint/stylelint/blob/main/CHANGELOG.md)
- [Commits](stylelint/stylelint@13.5.0...13.13.1)

---
updated-dependencies:
- dependency-name: flatted
  dependency-version: 3.4.2
  dependency-type: indirect
- dependency-name: stylelint
  dependency-version: 13.13.1
  dependency-type: direct:development
...

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Author: dependabot[bot]