fix: /etc/default/grub VHD enforcement

[jackfrancis]

Reason for Change:

#1111 included a bug in VHD /etc/default/grub enforcement

Issue Fixed:

Follow up from #1111

Requirements:

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

Notes:

[CecileRobertMichon]

/lgtm

[acs-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: CecileRobertMichon, jackfrancis

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[codecov]

Codecov Report

Merging #1131 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1131   +/-   ##
=======================================
  Coverage   74.39%   74.39%           
=======================================
  Files         131      131           
  Lines       18287    18287           
=======================================
  Hits        13604    13604           
  Misses       3902     3902           
  Partials      781      781