statistics: fix wrong singleflight implementation for stats' syncload

[hawkingrei]

What problem does this PR solve?

Issue Number: close #52294

Problem Summary:

What changed and how does it work?

the problem has been described in the issue. we refactor the singleflight using the golang official library.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No need to test

  • I checked and no code files have been changed.

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[hawkingrei]

/retest

[hawkingrei]

/retest

[hawkingrei]

@elsa0520 @hi-rustin PTAL

[elsa0520]

LGTM

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: elsa0520, tangenta, winoros

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[hawkingrei]

/unhold

[hawkingrei]

/cherrypick release-7.5

[ti-chi-bot]

@hawkingrei: new pull request created to branch release-7.5: #52374.

In response to this:

/cherrypick release-7.5

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.

[hawkingrei]

/cherrypick release-7.1
/cherrypick release-6.5

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #52382.

[ti-chi-bot]

@hawkingrei: new pull request created to branch release-6.5: #52383.

In response to this:

/cherrypick release-7.1
/cherrypick release-6.5

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]

@hawkingrei: new pull request could not be created: failed to create pull request against pingcap/tidb#release-7.1 from head ti-chi-bot:cherry-pick-52301-to-release-7.1: status code 422 not one of [201], body: {"message":"Validation Failed","errors":[{"resource":"PullRequest","code":"custom","message":"A pull request already exists for ti-chi-bot:cherry-pick-52301-to-release-7.1."}],"documentation_url":"https://docs.github.com/rest/pulls/pulls#create-a-pull-request"}

In response to this:

/cherrypick release-7.1
/cherrypick release-6.5

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.