Bump handlebars from 4.5.3 to 4.7.3 in /build

Bumps [handlebars](https://github.com/wycats/handlebars.js) from 4.5.3 to 4.7.3.
- [Release notes](https://github.com/wycats/handlebars.js/releases)
- [Changelog](https://github.com/wycats/handlebars.js/blob/master/release-notes.md)
- [Commits](https://github.com/wycats/handlebars.js/compare/v4.5.3...v4.7.3

)

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