*: fix scheduling can not immediately start after transfer leader (#4875)

[ti-chi-bot]

This is an automated cherry-pick of #4875

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

What problem does this PR solve?

Issue Number: Close #4769.

What is changed and how does it work?

This PR uses the flag to distinguish if the region's heartbeat is new when transferring the PD leader.

Check List

Tests

• Unit test

Release note

Fix the issue that scheduling cannot immediately start after PD leader transfers

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• nolouch
• rleungx

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[codecov]

Codecov Report

Merging #4970 (07a24c2) into release-5.4 (9473328) will increase coverage by 0.14%.
The diff coverage is 88.00%.

@@               Coverage Diff               @@
##           release-5.4    #4970      +/-   ##
===============================================
+ Coverage        74.84%   74.99%   +0.14%     
===============================================
  Files              265      265              
  Lines            27976    27989      +13     
===============================================
+ Hits             20938    20989      +51     
+ Misses            5176     5154      -22     
+ Partials          1862     1846      -16     

Flag	Coverage Δ
unittests	74.99% <88.00%> (+0.14%)	⬆️

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

Impacted Files	Coverage Δ
server/region_syncer/client.go	83.72% <50.00%> (+4.81%)	⬆️
server/cluster/cluster.go	82.95% <85.71%> (+0.55%)	⬆️
server/cluster/coordinator.go	74.36% <100.00%> (-0.32%)	⬇️
server/core/region.go	91.90% <100.00%> (+0.04%)	⬆️
server/core/region_option.go	82.85% <100.00%> (+0.33%)	⬆️
server/grpc_service.go	51.69% <100.00%> (-0.20%)	⬇️
pkg/errs/errs.go	75.00% <0.00%> (-25.00%)	⬇️
pkg/tempurl/tempurl.go	45.00% <0.00%> (-15.00%)	⬇️
pkg/cache/lru.go	79.06% <0.00%> (-9.31%)	⬇️
... and 16 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: 6038a45

[ti-chi-bot]

@ti-chi-bot: Your PR was out of date, I have automatically updated it for you.

At the same time I will also trigger all tests for you:

/run-all-tests

If the CI test fails, you just re-trigger the test that failed and the bot will merge the PR for you after the CI passes.

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