region_scatterer: fix the bug that could generate schedule with too many peers

[HunDunDM]

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:

• lhy1024
• rleungx

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[codecov]

Codecov Report

Base: 75.43% // Head: 75.42% // Decreases project coverage by -0.01% ⚠️

Coverage data is based on head (6b78c7d) compared to base (7497e3d).
Patch coverage: 100.00% of modified lines in pull request are covered.

❗ Current head 6b78c7d differs from pull request most recent head 40521b7. Consider uploading reports for the commit 40521b7 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5920      +/-   ##
==========================================
- Coverage   75.43%   75.42%   -0.01%     
==========================================
  Files         345      345              
  Lines       35126    35127       +1     
==========================================
  Hits        26496    26496              
- Misses       6330     6334       +4     
+ Partials     2300     2297       -3     

Flag	Coverage Δ
unittests	75.42% <100.00%> (-0.01%)	⬇️

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

Impacted Files	Coverage Δ
server/schedule/region_scatterer.go	79.13% <100.00%> (+0.08%)	⬆️
pkg/storage/endpoint/meta.go	63.63% <0.00%> (-4.55%)	⬇️
pkg/storage/kv/etcd_kv.go	72.22% <0.00%> (-3.18%)	⬇️
pkg/election/leadership.go	75.25% <0.00%> (-3.10%)	⬇️
pkg/dashboard/adapter/manager.go	79.31% <0.00%> (-2.30%)	⬇️
server/schedule/operator_controller.go	85.97% <0.00%> (-0.91%)	⬇️
server/grpc_service.go	48.70% <0.00%> (-0.65%)	⬇️
server/statistics/store_collection.go	93.75% <0.00%> (-0.63%)	⬇️
server/cluster/cluster.go	81.42% <0.00%> (-0.52%)	⬇️
server/server.go	74.14% <0.00%> (-0.38%)	⬇️
... and 10 more

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[HunDunDM]

/merge

[ti-chi-bot]

@HunDunDM: 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: 40521b7

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.5: #5923.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-5.0: #5924.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-5.1: #5925.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-5.2: #5926.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-5.3: #5927.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-5.4: #5928.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.1: #5929.