Disable libmi dependent tests for macOS.

[PaulHigin]

PR Summary

Disable tests on macOS that depend on the libmi library we ship.

PR Context

The latest version of macOS is not compatible with the libmi library we ship, and is causing some remoting tests to fail.
This PR disables those tests for macOS only.

PR Checklist

• PR has a meaningful title
  • Use the present tense and imperative mood when describing your changes
• Summarized changes
• 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.
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• Breaking changes
  • None
  • OR
  • Experimental feature(s) needed
    • Experimental feature name(s):
• User-facing changes
  • Not Applicable
  • OR
  • Documentation needed
    • Issue filed:
• Testing - New and feature
  • N/A 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
• Tooling
  • I have considered the user experience from a tooling perspective and don't believe tooling will be impacted.
  • OR
  • I have considered the user experience from a tooling perspective and enumerated concerns in the summary. This may include:
    • Impact on PowerShell Editor Services which is used in the PowerShell extension for VSCode (which runs in a different PS Host).
    • Impact on Completions (both in the console and in editors) - one of PowerShell's most powerful features.
    • Impact on PSScriptAnalyzer (which provides linting & formatting in the editor extensions).
    • Impact on EditorSyntax (which provides syntax highlighting with in VSCode, GitHub, and many other editors).

[TravisEz13]

Definitely needed for 7.1, probably for 7.0.

[ghost]

🎉v7.0.4 has been released which incorporates this pull request.:tada:

Handy links:

• Release Notes

[ghost]

🎉v7.2.0-preview.3 has been released which incorporates this pull request.:tada:

Handy links:

• Release Notes