ADGroup: Fix Child Domain User Membership

[X-Guardian]

Pull Request (PR) description

This PR fixes the issue where managing child domain user membership of an AD Group using the DistinguishedName MembershipAttribute fails.

This Pull Request (PR) fixes the following issues

• Fixes ADGroup: Cannot Manage Child Domain User Membership Using DistinguishedName in v6.1.0-preview0006 #633

Task list

• Added an entry to the change log under the Unreleased section of the
  file CHANGELOG.md. Entry should say what was changed and how that
  affects users (if applicable), and reference the issue being resolved
  (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 Community Testing Guidelines.
• Integration tests added/updated (where possible). See DSC Community Testing Guidelines.
• New/changed code adheres to DSC Community Style Guidelines.

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This change is 

[X-Guardian]

/azp run dsccommunity.ActiveDirectoryDsc

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[stale]

Labeling this pull request (PR) as abandoned since it has gone 14 days or more since the last update. An abandoned PR can be continued by another contributor. The abandoned label will be removed if work on this PR is taken up again.

[stale]

Labeling this pull request (PR) as abandoned since it has gone 14 days or more since the last update. An abandoned PR can be continued by another contributor. The abandoned label will be removed if work on this PR is taken up again.