fix: return nil err when there are no healthchecks

[fuskovic]

Closes: #5045

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[codecov]

Codecov Report

❌ Patch coverage is 96.87500% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 55.13%. Comparing base (9cd0158) to head (c7e32d8).
⚠️ Report is 17 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/controller/stages/regular_stages.go	96.87%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5093      +/-   ##
==========================================
+ Coverage   55.07%   55.13%   +0.05%     
==========================================
  Files         400      401       +1     
  Lines       35205    35661     +456     
==========================================
+ Hits        19390    19662     +272     
- Misses      14865    15038     +173     
- Partials      950      961      +11     

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[krancour]

@fuskovic apart from #5093 (comment), please just give this an e2e test-drive to make sure you don't get stuck reconciling if:

• Stage hasn't had any Promotions yet F.H.
• A Promotion is currently in-progress F.H.
• Last Promotion failed F.H.
• Last Promotion succeeded but didn't have any health checks (you can do this by not involving Argo CD in your promotion process) F.H.

After that sanity check, this looks g2g.

[krancour]

I've discovered a new bug this introduces. If health assesses to Unknown, it will block verification indefinitely.

I'm thinking about the best way to deal with this...

[krancour]

Closing this. Explanation here: #5045 (comment)