build(deps): bump @ckeditor/ckeditor5-build-classic

Bumps [@ckeditor/ckeditor5-build-classic](https://github.com/ckeditor/ckeditor5/tree/HEAD/packages/ckeditor5-build-classic) from 40.0.0 to 43.1.0.
- [Release notes](https://github.com/ckeditor/ckeditor5/releases)
- [Changelog](https://github.com/ckeditor/ckeditor5/blob/master/CHANGELOG.md)
- [Commits](https://github.com/ckeditor/ckeditor5/commits/v43.1.0/packages/ckeditor5-build-classic)

---
updated-dependencies:
- dependency-name: "@ckeditor/ckeditor5-build-classic"
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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