Minor refactoring of the CSV output

[olegbespalov]

What?

This pull request fixes the linter issues in the output/CSV package.

Why?

As we agreed, we aim to fix most of the linter issues.

Checklist

• I have performed a self-review of my code.
• I have added tests for my changes.
• I have run linter locally (make lint) and all checks pass.
• I have run tests locally (make tests) and all tests pass.
• I have commented on my code, particularly in hard-to-understand areas.

Related PR(s)/Issue(s)

Part of #769

[codecov-commenter]

Codecov Report

Attention: 7 lines in your changes are missing coverage. Please review.

Comparison is base (a087d42) 73.23% compared to head (7e743a6) 73.22%.

❗ Current head 7e743a6 differs from pull request most recent head 7b774ce. Consider uploading reports for the commit 7b774ce to get more accurate results

Files	Patch %	Lines
output/csv/output.go	65.00%	4 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3462      +/-   ##
==========================================
- Coverage   73.23%   73.22%   -0.01%     
==========================================
  Files         267      267              
  Lines       20083    20087       +4     
==========================================
+ Hits        14707    14709       +2     
  Misses       4463     4463              
- Partials      913      915       +2     

Flag	Coverage Δ
ubuntu	73.15% <66.66%> (-0.01%)	⬇️
windows	73.07% <66.66%> (+<0.01%)	⬆️

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[codebien]

Well done, thanks!