server: fix the leader cannot election after pd leader lost while etcd leader intact (#6447)

[ti-chi-bot]

This is an automated cherry-pick of #6447

What problem does this PR solve?

Issue Number: Close #6403

What is changed and how does it work?

server: fix the leader cannot election after pd leader lost while etcd leader intact

Check List

Tests

• Unit test
• Integration test

Release note

None.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• JmPotato
• nolouch

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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: fd87b5a

[ti-chi-bot]

@ti-chi-bot: Your PR was out of date, I have automatically updated it for you.

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[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.10 ⚠️

Comparison is base (c7db3b3) 75.71% compared to head (fd87b5a) 75.61%.

❗ Current head fd87b5a differs from pull request most recent head 26a456b. Consider uploading reports for the commit 26a456b to get more accurate results

Additional details and impacted files

@@               Coverage Diff               @@
##           release-6.5    #6460      +/-   ##
===============================================
- Coverage        75.71%   75.61%   -0.10%     
===============================================
  Files              330      330              
  Lines            33017    33046      +29     
===============================================
- Hits             24998    24989       -9     
- Misses            5873     5896      +23     
- Partials          2146     2161      +15     

Flag	Coverage Δ
unittests	75.61% <100.00%> (-0.10%)	⬇️

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

Impacted Files	Coverage Δ
server/member/member.go	66.83% <100.00%> (+1.04%)	⬆️
server/server.go	75.57% <100.00%> (+0.94%)	⬆️

... and 25 files with indirect coverage changes

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