mcs: fix checkMembershipCh blocking

[lhy1024]

What problem does this PR solve?

Issue Number: Close #7207

What is changed and how does it work?

After #7254, there are still stuck TestHot because of blocking channel

Check List

Tests

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

for i in {1..20}
do
	go test -run ^TestHotTestSuite$  github.com/tikv/pd/tests/pdctl/hot
done

Pass all

Release note

None.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• HuSharp
• rleungx

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[codecov]

Codecov Report

Merging #7272 (d7bb99f) into master (f9b476d) will increase coverage by 0.14%.
Report is 2 commits behind head on master.
The diff coverage is 80.00%.

❗ Current head d7bb99f differs from pull request most recent head 98c58e6. Consider uploading reports for the commit 98c58e6 to get more accurate results

@@            Coverage Diff             @@
##           master    #7272      +/-   ##
==========================================
+ Coverage   74.28%   74.43%   +0.14%     
==========================================
  Files         446      446              
  Lines       48227    48230       +3     
==========================================
+ Hits        35825    35898      +73     
+ Misses       9229     9169      -60     
+ Partials     3173     3163      -10     

Flag	Coverage Δ
unittests	74.43% <80.00%> (+0.14%)	⬆️

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[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

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[ti-chi-bot]

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

Commit hash: d7bb99f

[ti-chi-bot]

@lhy1024: Your PR was out of date, I have automatically updated it for you.

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.

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.