Bump elasticsearch from 7.8.1 to 7.9.0 (#14625)

Bumps [elasticsearch](https://github.com/elastic/elasticsearch-ruby) from 7.8.1 to 7.9.0.
- [Release notes](https://github.com/elastic/elasticsearch-ruby/releases)
- [Changelog](https://github.com/elastic/elasticsearch-ruby/blob/master/CHANGELOG.md)
- [Commits](https://github.com/elastic/elasticsearch-ruby/compare/v7.8.1...v7.9.0)

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