GHA: lint test is a prereq only for PR/main builds

[jsiirola]

Fixes # .

Summary/Motivation:

The linter test should only be a prerequisite for PRs and the main branch. User branch builds should proceed even if the linter fails: this should significantly reduce the number of NFC: apply black commits during development.

Changes proposed in this PR:

• Only preemptively fail PR/main builds based on a failed linter job

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[codecov]

Codecov Report

Patch coverage has no change and project coverage change: +0.20 🎉

Comparison is base (5417276) 86.96% compared to head (8d4e328) 87.17%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2818      +/-   ##
==========================================
+ Coverage   86.96%   87.17%   +0.20%     
==========================================
  Files         764      764              
  Lines       88262    88262              
==========================================
+ Hits        76761    76940     +179     
+ Misses      11501    11322     -179     

Flag	Coverage Δ
linux	84.22% <ø> (+<0.01%)	⬆️
osx	73.86% <ø> (+<0.01%)	⬆️
other	84.40% <ø> (+0.19%)	⬆️
win	81.76% <ø> (?)

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see 2 files with indirect coverage changes

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