statistics: fix data race in `IsRegionHot`

[lhy1024]

What problem does this PR solve?

Issue Number: Close #8335

Before #8164 it is

// IsRegionHot checks if the region is hot.
func (w *HotCache) IsRegionHot(region *core.RegionInfo, minHotDegree int) bool {
    checkRegionHotWriteTask := newCheckRegionHotTask(region, minHotDegree)
    checkRegionHotReadTask := newCheckRegionHotTask(region, minHotDegree)
    succ1 := w.CheckWriteAsync(checkRegionHotWriteTask)
    succ2 := w.CheckReadAsync(checkRegionHotReadTask)
    if succ1 && succ2 {
        return checkRegionHotWriteTask.waitRet(w.ctx) || checkRegionHotReadTask.waitRet(w.ctx)
    }
    return false
}

What is changed and how does it work?

Check List

Tests

• Unit test

• Test1: This test will meet data race in master and is normal in this PR.

  
  for i in {1..50}; do
  go clean -testcache
  go test -timeout 120s -run ^TestSpecialUseHotRegion$ github.com/tikv/pd/pkg/schedule/schedulers -race
  done

- Test2:
This test will be successful in this PR and be failed in master branches

--- FAIL: TestIsHot (0.00s) /home/lhy1024/pd/pkg/statistics/hot_cache_test.go:34: Error Trace: /home/lhy1024/pd/pkg/statistics/hot_cache_test.go:34 Error: Should be true Test: TestIsHot FAIL

### Release note

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```release-note
None.

[HuSharp]

CI can find the data race problem, but it's strange why it hasn't been found in two weeks.

[ti-chi-bot[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: HuSharp, rleungx

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Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/tikv/pd/blob/master/OWNERS)~~ [HuSharp,rleungx] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[ti-chi-bot[bot]]

[LGTM Timeline notifier]

Timeline:

• 2024-06-27 07:41:34.356528884 +0000 UTC m=+878220.842017713: :ballot_box_with_check: agreed by rleungx.
• 2024-06-27 08:16:53.20871402 +0000 UTC m=+880339.694202852: :ballot_box_with_check: agreed by HuSharp.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.2: #8341.

[HuSharp]

CI can find the data race problem, but it's strange why it hasn't been found in two weeks.

fixed in https://github.com/tikv/pd/pull/8342