AboutAssertions - Avoid Casting [Blank] to [bool]

[vexx32]

PR Summary

PS's built-in boolean-casting behaviour cannot be overridden for reference types casting to bool, so any assertion that results in $blank | Should -BeTrue where $blank is an instance of [Blank] (obtained usually from Get-Blank / __ / ____) will automatically pass.

The usual fix is to avoid framing assertions in this way.

Context

Resolves #315

Changes

• Reframe affected assertions to avoid the casting behaviour.
• Update parts of the intstruction comments.

Checklist

• Pull Request has a meaningful title.
• Summarised changes.
• Pull Request is ready to merge & is not WIP.
• Added tests / only testable interactively.
  • Make sure you add a new test if old tests do not effectively test the code changed.
• Added documentation / opened issue to track adding documentation at a later date.