descheduler: change the order of check len(lowNodes) and len(sourceNodes)

[bogo-y]

Ⅰ. Describe what this PR does

We firstly check len(lowNodes) after classifyNodes, which cloud lead to the sourceNodes lose a chance to be mark as abnormal. If we change the order, the sourceNodes cloud be evict more quickly when we just add a new node to a overloaded cluster.

Ⅱ. Does this pull request fix one issue?

Ⅲ. Describe how to verify it

Ⅳ. Special notes for reviews

V. Checklist

• I have written necessary docs and comments
• I have added necessary unit tests and integration tests
• All checks passed in make test

[codecov]

Codecov Report

Attention: Patch coverage is 55.55556% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 67.52%. Comparing base (beaafa3) to head (40a0a08).
Report is 1 commits behind head on main.

Files	Patch %	Lines
...duler/framework/plugins/loadaware/low_node_load.go	55.55%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1957   +/-   ##
=======================================
  Coverage   67.52%   67.52%           
=======================================
  Files         420      420           
  Lines       47040    47047    +7     
=======================================
+ Hits        31764    31769    +5     
- Misses      12965    12971    +6     
+ Partials     2311     2307    -4     

Flag	Coverage Δ
unittests	67.52% <55.55%> (+<0.01%)	⬆️

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[eahydra]

/lgtm

[eahydra]

please add signature with command git commit -s --amend --no-edit

[bogo-y]

/retest-required

[koordinator-bot]

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/retest-required

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[eahydra]

/lgtm
/approve

[koordinator-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: eahydra

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