Fix the test matrix

[Jaykul]

Remove outdated github actions

[Jaykul]

It turns out that zyborg/pester-tests-report can't do Pester 4 so ... I upgraded all the tests to Pester 5

[Jaykul]

Worse. It turns out the zyborg/pester-tests-report can't handle how big our test report would be. Ugh.

However, on top of that the Parameters.Tests.ps1 are still failing -- and they only fail in the test matrix, not in the initial build, nor in earthly (nor on my computer, obviously). I don't know what's happening there yet.

[Jaykul]

OK. It took me a lot longer to figure that out than I would have liked, and too many attempts to fix it, but it turns out the problem with the test matrix was basically the fact that we use ModuleBuilder to build ModuleBuilder.

In the main build we use Invoke-Build and are very careful to import the right module for testing, but in the test matrix the tests were running against the installed copy instead of the newly built version.