[release-20.0-rc] VDiff CLI: Fix VDiff show bug (#16177)

[vitess-bot]

Description

This is a backport of #16177

[vitess-bot]

Review Checklist

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General

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[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 68.50%. Comparing base (4865893) to head (467397a).
Report is 2 commits behind head on release-20.0-rc.

Files	Patch %	Lines
...d/vtctldclient/command/vreplication/vdiff/vdiff.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@                 Coverage Diff                 @@
##           release-20.0-rc   #16199      +/-   ##
===================================================
+ Coverage            68.47%   68.50%   +0.03%     
===================================================
  Files                 1541     1541              
  Lines               197614   197625      +11     
===================================================
+ Hits                135314   135385      +71     
+ Misses               62300    62240      -60     

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