Fix Ubuntu build and runspace test by bergmeister · Pull Request #1340 · PowerShell/PSScriptAnalyzer

PR Summary

Bringing back my old code to bootstrap the .Net SDK in CI because it works. To me that -bootstrap is over-engineered and therefore hard to debug and does not even work well (it does not persist after closing the shell on Windows, therefore I do not use it for development anyway...)
As part of it it discovered a new test assertion failure (wrong expectation) that it fixes as well.

PR Checklist

• PR has a meaningful title
  • Use the present tense and imperative mood when describing your changes
• Summarized changes
• Change is not breaking
• Make sure all .cs, .ps1 and .psm1 files have the correct copyright header
• Make sure you've added a new test if existing tests do not effectively test the code changed and/or updated documentation
• This PR is ready to merge and is not Work in Progress.
  • If the PR is work in progress, please add the prefix WIP: to the beginning of the title and remove the prefix when the PR is ready.