Skip tests on Appveyor due to PSReadline issue - #8317

PR Summary

Enter-PSHostProcess tests fail on AppVeyor due to PSReadline issue. This change skips the tests on AppVeyor.

Expected 3948, but got @(<empty>, 'Oops, something went wrong.  Please report this bug with the details below.', 'Report on GitHub: https://github.com/lzybkr/PSReadLine/issues/new', '-----------------------------------------------------------------------', 'Last 0 Keys:', '```', <empty>, '```', <empty>, 'Exception:').

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 .h, .cpp, .cs, .ps1 and .psm1 files have the correct copyright header
• 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.
• User-facing changes
  • Not Applicable
  • OR
  • User-facing Documentation needed
    • Issue filed - Issue link:
• Testing - New and feature
  • Not Applicable or can only be tested interactively
  • OR
  • Make sure you've added a new test if existing tests do not effectively test the code changed
    • Add [feature] if the change is significant or affects feature tests