Assert-BlockString: Allow string array and single string for Expected

[johlju]

Pull Request (PR) description

• Assert-BlockString
  • Allow it to pass string array and single string to Expected parameter.

This Pull Request (PR) fixes the following issues

None.

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).
• Documentation added/updated in README.md and source/WikiSource.
• Comment-based help added/updated for all new/changed functions.
• 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 applicable). See
  DSC Community Testing Guidelines.
• New/changed code adheres to DSC Community Style Guidelines.

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This change is 

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78%. Comparing base (9d3a7eb) to head (d441c24).
Report is 2 commits behind head on main.

Additional details and impacted files

@@        Coverage Diff         @@
##           main    #3   +/-   ##
==================================
+ Coverage    75%   78%   +3%     
==================================
  Files         2     2           
  Lines        20    23    +3     
==================================
+ Hits         15    18    +3     
  Misses        5     5           

Flag	Coverage Δ
unit	78% <100%> (+3%)	⬆️

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Files	Coverage Δ
source/Public/Assert-BlockString.ps1	100% <100%> (ø)