Bumps [retrofit](https://github.com/square/retrofit) from 1.6.1 to 1.9.0. - [Release notes](https://github.com/square/retrofit/releases) - [Changelog](https://github.com/square/retrofit/blob/master/CHANGELOG.md) - [Commits](https://github.com/square/retrofit/compare/parent-1.6.1...parent-1.9.0) Signed-off-by: dependabot-preview[bot] <support@dependabot.com>