Remove the use of deprecated BroadcastChannel.

[romkal]

Description

It seems like the BroadcastChannel is completely deprecated in the newest Kotlin, so.. getting rid of it.

It is effectively a refactoring as it touches only the test code.

Type of Change

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update

Test Plan

Just run the current tests.

Checklist:

Before submitting your PR, please review and check all of the following:

• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] I have added tests that prove my change is effective
• [x] New and existing unit tests pass locally with my changes

Additional Notes:

Add any other information about the PR here.