cluster: fix the merging issue of labels after store reboot (#6468)

[ti-chi-bot]

This is an automated cherry-pick of #6468

What problem does this PR solve?

Issue Number: Close #6467.

What is changed and how does it work?

#5510 introduced a bug that would cause the store labels to be overwritten wrongly after the store reboot.
This PR fixed this issue.

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: ac435f4