statistics: fix data race in `IsRegionHot` (#8336)

This is an automated cherry-pick of #8336

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

<!--

A bugfix or a new feature needs a release note. If there is no need to give a release note, just leave it with the `None`.

Please refer to [Release Notes Language Style Guide](https://pingcap.github.io/tidb-dev-guide/contribute-to-tidb/release-notes-style-guide.html) to write a quality release note.

-->

```release-note
None.

tikv / pd

statistics: fix data race in `IsRegionHot` (#8336) #8341

What problem does this PR solve?

What is changed and how does it work?

Check List