MudStepper: Fix CompletedContent not shown in Vertical variant

[henon]

Description

CompletedContent isn't shown for stepper in Vertical mode
Resolves #10047

How Has This Been Tested?

unit | visually

Type of Changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation (fix or improvement to the website or code docs)

Checklist

• The PR is submitted to the correct branch (dev).
• My code follows the code style of this project.
• I've added relevant tests.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.13%. Comparing base (3a8849c) to head (0a9a312).
Report is 2 commits behind head on dev.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev   #10075   +/-   ##
=======================================
  Coverage   91.13%   91.13%           
=======================================
  Files         411      411           
  Lines       12482    12482           
  Branches     2422     2422           
=======================================
  Hits        11376    11376           
  Misses        560      560           
  Partials      546      546           

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[ScarletKuro]

Do want this in v7?

[henon]

#10047

Yes, it is a blatant oversight