Bump laravel/horizon from 5.21.2 to 5.21.3

Bumps [laravel/horizon](https://github.com/laravel/horizon) from 5.21.2 to 5.21.3.
- [Release notes](https://github.com/laravel/horizon/releases)
- [Changelog](https://github.com/laravel/horizon/blob/5.x/CHANGELOG.md)
- [Commits](laravel/horizon@v5.21.2...v5.21.3)

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

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