[githubgen] PR feedback follow-ups

[mowies]

Follow up to #639

[codecov]

Codecov Report

Attention: Patch coverage is 53.92157% with 47 lines in your changes missing coverage. Please review.

Project coverage is 50.33%. Comparing base (fcfa1a6) to head (f714d4d).
Report is 11 commits behind head on main.

Files with missing lines	Patch %	Lines
githubgen/codeowners.go	65.07%	21 Missing and 1 partial ⚠️
githubgen/main.go	14.28%	18 Missing ⚠️
githubgen/issuetemplates.go	61.11%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #655      +/-   ##
==========================================
+ Coverage   47.13%   50.33%   +3.20%     
==========================================
  Files          56       57       +1     
  Lines        3214     3401     +187     
==========================================
+ Hits         1515     1712     +197     
+ Misses       1548     1527      -21     
- Partials      151      162      +11     

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