Add tests for kubernetes versions

[pdabelf5]

Proposed changes

• Add unit tests for k8s version validation
• Switch to returning an error from validateKubernetesVersionInfo() to make the function testable.

This is a similar approach to #5110, but in smaller changes.

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 4 lines in your changes missing coverage. Please review.

Project coverage is 52.76%. Comparing base (2e0daa1) to head (5a9ec4e).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/nginx-ingress/main.go	50.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7035      +/-   ##
==========================================
+ Coverage   52.73%   52.76%   +0.03%     
==========================================
  Files          89       89              
  Lines       20824    20827       +3     
==========================================
+ Hits        10981    10990       +9     
+ Misses       9389     9380       -9     
- Partials      454      457       +3     

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