ci: make sure sku is exact match when deciding to create or reuse sku for publishing Windows VHDs

[marosset]

Reason for Change:

AKS publishes SKUs starting with aks- and if AKS publishes a SKU first the logic in this script will not create a new non-AKS sku so I'm fixing that.

Issue Fixed:

Credit Where Due:

Does this change contain code from or inspired by another project?

• No
• Yes

If "Yes," did you notify that project's maintainers and provide attribution?

• No
• Yes

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Notes:

[jsturtevant]

/lgtm

[acs-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jsturtevant, marosset

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[codecov]

Codecov Report

Merging #4292 (61c04e5) into master (2e1052a) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #4292   +/-   ##
=======================================
  Coverage   72.03%   72.03%           
=======================================
  Files         141      141           
  Lines       21633    21633           
=======================================
  Hits        15584    15584           
  Misses       5099     5099           
  Partials      950      950           

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