GUILD-569: Ensuring lingering sent messages are cleared before tests setup

[eduardopoleoflipp]

Pull Request Template

Description

This ensures that we do not accidentally delete messages that have been set up for the currently running test.

Fixes #89

Type of change

Please delete options that are not relevant.

• [x] Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• [ ] Unit + Integrations tests pass

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [x] I have added a line in the CHANGELOG describing this change, under the UNRELEASED heading
• [x] My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes
• [ ] Any dependent changes have been merged and published in downstream modules

[dorner]

Thanks!