Bump flatted and karma in /src/admin/assets/components/bootstrap

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


Updates `flatted` from 2.0.0 to 3.4.2
- [Commits](WebReflection/flatted@v2.0.0...v3.4.2)

Updates `karma` from 3.1.4 to 6.4.4
- [Release notes](https://github.com/karma-runner/karma/releases)
- [Changelog](https://github.com/karma-runner/karma/blob/master/CHANGELOG.md)
- [Commits](karma-runner/karma@v3.1.4...v6.4.4)

---
updated-dependencies:
- dependency-name: flatted
  dependency-version: 3.4.2
  dependency-type: indirect
- dependency-name: karma
  dependency-version: 6.4.4
  dependency-type: direct:development
...

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Author: dependabot[bot]