region_scatterer: fix the bug that could generate schedule with too many peers (#5920)

[ti-chi-bot]

This is an automated cherry-pick of #5920

What problem does this PR solve?

Issue Number: Close #5909

What is changed and how does it work?

Introduced in #4570 , used stores were not excluded resulting in possible selection of too many targeterPeers.

Check List

Tests

• Unit test

Code changes

Side effects

Related changes

• Need to cherry-pick to the release branch

Release note

Fix the bug that the region scatterer may generate the schedule with too many peers.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• CabinfeverB
• lhy1024

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[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.14 🎉

Comparison is base (a6e77c1) 75.34% compared to head (6a31075) 75.49%.

❗ Current head 6a31075 differs from pull request most recent head 7d7211c. Consider uploading reports for the commit 7d7211c to get more accurate results

Additional details and impacted files

@@               Coverage Diff               @@
##           release-6.1    #5929      +/-   ##
===============================================
+ Coverage        75.34%   75.49%   +0.14%     
===============================================
  Files              307      307              
  Lines            30480    30481       +1     
===============================================
+ Hits             22965    23011      +46     
+ Misses            5506     5480      -26     
+ Partials          2009     1990      -19     

Flag	Coverage Δ
unittests	75.49% <100.00%> (+0.14%)	⬆️

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

Impacted Files	Coverage Δ
server/schedule/region_scatterer.go	82.80% <100.00%> (+0.06%)	⬆️

... and 27 files with indirect coverage changes

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[CabinfeverB]

/merge

[ti-chi-bot]

@CabinfeverB: It seems you want to merge this PR, I will help you trigger all the tests:

/run-all-tests

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[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 6a31075

[ti-chi-bot]

@ti-chi-bot: Your PR was out of date, I have automatically updated it for you.

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