Update github-markup requirement from ~> 3.0 to ~> 4.0
Update github-markup requirement from ~> 3.0 to ~> 4.0

Updates the requirements on [github-markup](https://github.com/github/markup) to permit the latest version.
- [Release notes](https://github.com/github/markup/releases)
- [Changelog](https://github.com/github/markup/blob/master/HISTORY.md)
- [Commits](https://github.com/github/markup/compare/v3.0.0...v4.0.0)

Signed-off-by: dependabot-preview[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>
sensu-plugins/sensu-plugins-postgres