build: Bump laravel/horizon from 5.19.2 to 5.20.0 (#3231)

Bumps [laravel/horizon](https://github.com/laravel/horizon) from 5.19.2 to 5.20.0.
- [Release notes](https://github.com/laravel/horizon/releases)
- [Changelog](https://github.com/laravel/horizon/blob/5.x/CHANGELOG.md)
- [Commits](laravel/horizon@v5.19.2...v5.20.0)

---
updated-dependencies:
- dependency-name: laravel/horizon
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>