EXOManagementRoleAssignment - Drift Detection Fix

[NikCharlebois]

Pull Request (PR) description

• EXOManagementRoleAssignment
  • Changed logic to detect drift.

This Pull Request (PR) fixes the following issues

• N/A

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 parameter descriptions added/updated in the schema.mof.
• Resource documentation added/updated in README.md.
• Resource settings.json file contains all required permissions.
• Examples appropriately added/updated.
• Unit tests added/updated.
• New/changed code adheres to DSC Community Style Guidelines.