leadership: avoid potential data race (#6636)

[ti-chi-bot]

This is an automated cherry-pick of #6636

What problem does this PR solve?

Issue Number: Close #6635

What is changed and how does it work?

Check List

Tests

• Unit test

Release note

None.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• HuSharp
• bufferflies

To complete the pull request process, please ask the reviewers in the list to review by filling /cc @reviewer in the comment.
After your PR has acquired the required number of LGTMs, you can assign this pull request to the committer in the list by filling /assign @committer in the comment to help you merge this pull request.

The full list of commands accepted by this bot can be found here.

Reviewer can indicate their review by submitting an approval review.
Reviewer can cancel approval by submitting a request changes review.

[codecov]

Codecov Report

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

Comparison is base (cb1af02) 74.88% compared to head (f415707) 74.78%.

Additional details and impacted files

@@               Coverage Diff               @@
##           release-5.4    #6703      +/-   ##
===============================================
- Coverage        74.88%   74.78%   -0.10%     
===============================================
  Files              265      265              
  Lines            28008    28012       +4     
===============================================
- Hits             20974    20950      -24     
- Misses            5187     5211      +24     
- Partials          1847     1851       +4     

Flag	Coverage Δ
unittests	74.78% <100.00%> (-0.10%)	⬇️

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

Impacted Files	Coverage Δ
server/election/leadership.go	78.21% <100.00%> (+0.89%)	⬆️
server/server.go	71.68% <100.00%> (-1.20%)	⬇️

... and 11 files with indirect coverage changes

☔ View full report in Codecov by Sentry.
📢 Do you have feedback about the report comment? Let us know in this issue.

[lhy1024]

/merge

[ti-chi-bot]

@lhy1024: It seems you want to merge this PR, I will help you trigger all the tests:

/run-all-tests

You only need to trigger /merge once, and 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.

If you have any questions about the PR merge process, please refer to pr process.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: f415707