replication_mode: fix the state cannot switch to async while existing learner node (#6452)

[ti-chi-bot]

This is an automated cherry-pick of #6452

What problem does this PR solve?

Issue Number: ref #4399 Close tikv/tikv#14704

What is changed and how does it work?

replication_mode: fix the state cannot switch to async while existing learner node
 - skip the learner node when check the stores state

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

Release note

None.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• nolouch

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[codecov]

Codecov Report

Patch coverage: 94.73% and project coverage change: -0.01 ⚠️

Comparison is base (3a957d0) 74.95% compared to head (56d6dd5) 74.95%.

Additional details and impacted files

@@               Coverage Diff               @@
##           release-7.1    #6484      +/-   ##
===============================================
- Coverage        74.95%   74.95%   -0.01%     
===============================================
  Files              408      408              
  Lines            40683    40697      +14     
===============================================
+ Hits             30494    30504      +10     
+ Misses            7528     7523       -5     
- Partials          2661     2670       +9     

Flag	Coverage Δ
unittests	74.95% <94.73%> (-0.01%)	⬇️

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

Impacted Files	Coverage Δ
server/api/store.go	66.40% <66.66%> (+0.08%)	⬆️
pkg/core/basic_cluster.go	93.75% <100.00%> (ø)
pkg/core/region.go	88.97% <100.00%> (ø)
pkg/core/store.go	77.77% <100.00%> (+0.15%)	⬆️
pkg/core/store_option.go	100.00% <100.00%> (ø)
pkg/mock/mockcluster/mockcluster.go	94.74% <100.00%> (+0.03%)	⬆️
pkg/statistics/store_collection.go	89.20% <100.00%> (+0.25%)	⬆️
server/replication/replication_mode.go	78.94% <100.00%> (+0.13%)	⬆️

... and 31 files with indirect coverage changes

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[nolouch]

/merge

[ti-chi-bot]

@nolouch: 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: 56d6dd5