Bump flat and @ckeditor/ckeditor5-dev-utils in /django_ckeditor_5

Bumps [flat](https://github.com/hughsk/flat) to 5.0.2 and updates ancestor dependency [@ckeditor/ckeditor5-dev-utils](https://github.com/ckeditor/ckeditor5-dev/tree/HEAD/packages/ckeditor5-dev-utils). These dependencies need to be updated together.


Updates `flat` from 4.1.1 to 5.0.2
- [Release notes](https://github.com/hughsk/flat/releases)
- [Commits](hughsk/flat@4.1.1...5.0.2)

Updates `@ckeditor/ckeditor5-dev-utils` from 43.0.0 to 44.2.1
- [Release notes](https://github.com/ckeditor/ckeditor5-dev/releases)
- [Changelog](https://github.com/ckeditor/ckeditor5-dev/blob/master/CHANGELOG.md)
- [Commits](https://github.com/ckeditor/ckeditor5-dev/commits/v44.2.1/packages/ckeditor5-dev-utils)

---
updated-dependencies:
- dependency-name: flat
  dependency-type: indirect
- dependency-name: "@ckeditor/ckeditor5-dev-utils"
  dependency-type: direct:development
...

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