chore(deps-dev): bump handlebars from 4.1.2 to 4.2.1 in /core

Bumps [handlebars](https://github.com/wycats/handlebars.js) from 4.1.2 to 4.2.1.
- [Release notes](https://github.com/wycats/handlebars.js/releases)
- [Changelog](https://github.com/wycats/handlebars.js/blob/v4.2.1/release-notes.md)
- [Commits](handlebars-lang/handlebars.js@v4.1.2...v4.2.1)

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