cluster: reset stores cache before loading cluster info (#4942)

[ti-chi-bot]

This is an automated cherry-pick of #4942

Signed-off-by: Ryan Leung rleungx@gmail.com

What problem does this PR solve?

Issue Number: Close #4941.

What is changed and how does it work?

This PR resets the new leader store cache after transferring the PD leader.

Check List

Tests

• Unit test

Release note

Fix the issue that the removed tombstone store shows again after transferring the PD leader

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• nolouch
• rleungx

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[codecov]

Codecov Report

Merging #4955 (7fcbf52) into release-5.0 (961a7a0) will decrease coverage by 0.06%.
The diff coverage is 80.00%.

@@               Coverage Diff               @@
##           release-5.0    #4955      +/-   ##
===============================================
- Coverage        74.97%   74.90%   -0.07%     
===============================================
  Files              245      245              
  Lines            24463    24467       +4     
===============================================
- Hits             18341    18327      -14     
- Misses            4506     4515       +9     
- Partials          1616     1625       +9     

Flag	Coverage Δ
unittests	74.90% <80.00%> (-0.07%)	⬇️

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

Impacted Files	Coverage Δ
server/cluster/cluster.go	82.04% <50.00%> (-0.63%)	⬇️
server/core/basic_cluster.go	90.96% <100.00%> (+0.17%)	⬆️
pkg/dashboard/adapter/manager.go	82.97% <0.00%> (-7.45%)	⬇️
server/region_syncer/client.go	79.68% <0.00%> (-3.91%)	⬇️
server/schedulers/random_merge.go	60.00% <0.00%> (-3.34%)	⬇️
server/tso/tso.go	74.54% <0.00%> (-2.43%)	⬇️
server/core/storage.go	67.68% <0.00%> (-2.29%)	⬇️
server/schedule/operator/step.go	68.76% <0.00%> (-1.27%)	⬇️
server/server.go	71.21% <0.00%> (-1.05%)	⬇️
... and 10 more

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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: 8e853f7