fix(controller): replicas calculation for paused pipeline

[whynowy]

Explain what this PR does.

[codecov]

Codecov Report

Attention: Patch coverage is 12.50000% with 21 lines in your changes missing coverage. Please review.

Project coverage is 71.15%. Comparing base (ae6c2a6) to head (3c0fb9d).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/reconciler/pipeline/controller.go	25.00%	5 Missing and 1 partial ⚠️
pkg/reconciler/vertex/controller.go	14.28%	4 Missing and 2 partials ⚠️
pkg/reconciler/vertex/scaling/scaling.go	0.00%	5 Missing ⚠️
pkg/reconciler/monovertex/scaling/scaling.go	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2412      +/-   ##
==========================================
+ Coverage   71.03%   71.15%   +0.11%     
==========================================
  Files         368      368              
  Lines       53558    53575      +17     
==========================================
+ Hits        38047    38123      +76     
+ Misses      14435    14373      -62     
- Partials     1076     1079       +3     

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