Bump handlebars from 4.7.7 to 4.7.9 in /docs (#3025)

Bumps [handlebars](https://github.com/handlebars-lang/handlebars.js) from 4.7.7 to 4.7.9.
- [Release notes](https://github.com/handlebars-lang/handlebars.js/releases)
- [Changelog](https://github.com/handlebars-lang/handlebars.js/blob/v4.7.9/release-notes.md)
- [Commits](handlebars-lang/handlebars.js@v4.7.7...v4.7.9)

---
updated-dependencies:
- dependency-name: handlebars
  dependency-version: 4.7.9
  dependency-type: indirect
...

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