Added tests for the vt/logz package

[VaibhavMalik4187]

Description

This commit increases the code coverage of the go/vt/logz package to 100%.

Related Issue(s)

Partially Addresses: #14931

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

[vitess-bot]

Review Checklist

Hello reviewers! 👋 Please follow this checklist when reviewing this Pull Request.

General

• Ensure that the Pull Request has a descriptive title.
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• vtctl command output order should be stable and awk-able.

[VaibhavMalik4187]

@systay could you please review this PR whenever you have a moment? Thanks!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (f751c83) 47.49% compared to head (5115983) 47.54%.
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15060      +/-   ##
==========================================
+ Coverage   47.49%   47.54%   +0.05%     
==========================================
  Files        1149     1150       +1     
  Lines      239475   239614     +139     
==========================================
+ Hits       113730   113918     +188     
+ Misses     117138   117092      -46     
+ Partials     8607     8604       -3     

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[GuptaManan100]

LGTM!