check coreCount within AggregateCoreMetric

[justadogistaken]

What type of PR is this?

What this PR does / why we need it:

Which issue(s) this PR fixes:

Special notes for your reviewer:

[codecov]

Codecov Report

Attention: 23 lines in your changes are missing coverage. Please review.

Comparison is base (5652340) 53.17% compared to head (88533bb) 53.18%.
Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #320      +/-   ##
==========================================
+ Coverage   53.17%   53.18%   +0.01%     
==========================================
  Files         406      419      +13     
  Lines       43980    46297    +2317     
==========================================
+ Hits        23386    24625    +1239     
- Misses      18006    18884     +878     
- Partials     2588     2788     +200     

Flag	Coverage Δ
unittest	53.18% <73.25%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
pkg/agent/evictionmanager/podkiller/killer.go	64.40% <100.00%> (+0.20%)	⬆️
pkg/util/metric/store_util.go	88.88% <100.00%> (+0.31%)	⬆️
...advisor/qosaware/resource/memory/memory_advisor.go	62.06% <66.66%> (+0.53%)	⬆️
...advisor/qosaware/resource/memory/plugins/common.go	80.00% <80.00%> (ø)
...r/qosaware/resource/memory/plugins/cache_reaper.go	63.63% <63.63%> (ø)
...advisor/plugin/qosaware/resource/memory/advisor.go	80.31% <33.33%> (-1.37%)	⬇️
...in/qosaware/resource/memory/plugin/cache_reaper.go	84.48% <76.00%> (-6.83%)	⬇️

... and 42 files with indirect coverage changes

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