Updated pester test to support pester v5

[NicolasBn]

Pull Request (PR) description

Updated all pester test to support pester v5.

This Pull Request (PR) fixes the following issues

• Fixes part of issue Improve pester tests : increase Code coverage to 80%, migrate to pester v5 #73

Task list

• Added an entry under the Unreleased section of the change log in the CHANGELOG.md.
  Entry should say what was changed, and how that affects users (if applicable).
• Resource documentation added/updated in README.md.
• Resource parameter descriptions added/updated in README.md, schema.mof
  and comment-based help.
• Comment-based help added/updated.
• Localization strings added/updated in all localization files as appropriate.
• Examples appropriately added/updated.
• Unit tests added/updated. See DSC Resource Testing Guidelines.
• Integration tests added/updated (where possible). See DSC Resource Testing Guidelines.
• New/changed code adheres to DSC Resource Style Guidelines and Best Practices.

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This change is 

[gaelcolas]

Fixed a few things but it's smooth!