region_scatterer: fix incorrect test

[HunDunDM]

What problem does this PR solve?

close #4583

What is changed and how it works?

Check List

Tests

• Unit test

Code changes

Side effects

Related changes

Release note

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• JmPotato

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[JmPotato]

/merge

[ti-chi-bot]

@JmPotato: 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: 0462c60

[JmPotato]

/run-unit-test

[codecov]

Codecov Report

Merging #4586 (0462c60) into master (32832a3) will increase coverage by 0.11%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #4586      +/-   ##
==========================================
+ Coverage   74.83%   74.95%   +0.11%     
==========================================
  Files         265      265              
  Lines       27904    27908       +4     
==========================================
+ Hits        20883    20918      +35     
+ Misses       5154     5133      -21     
+ Partials     1867     1857      -10     

Flag	Coverage Δ
unittests	74.95% <100.00%> (+0.11%)	⬆️

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

Impacted Files	Coverage Δ
server/schedule/region_scatterer.go	83.19% <100.00%> (+0.28%)	⬆️
server/region_syncer/server.go	81.41% <0.00%> (-5.13%)	⬇️
server/id/id.go	76.19% <0.00%> (-4.77%)	⬇️
server/region_syncer/client.go	78.90% <0.00%> (-4.69%)	⬇️
pkg/etcdutil/etcdutil.go	84.70% <0.00%> (-1.18%)	⬇️
pkg/btree/btree.go	85.78% <0.00%> (-0.97%)	⬇️
server/server.go	71.85% <0.00%> (-0.90%)	⬇️
server/core/storage.go	69.31% <0.00%> (-0.76%)	⬇️
server/cluster/cluster.go	83.21% <0.00%> (-0.12%)	⬇️
server/tso/local_allocator.go	71.62% <0.00%> (ø)
... and 13 more

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[ti-chi-bot]

In response to a cherrypick label: new pull request created: #4587.