testScatterRegionSuite.TestScatterGroupInConcurrency is not stable

[HunDunDM]

Flaky Test

Which jobs are failing

FAIL: region_scatterer_test.go:295: testScatterRegionSuite.TestScatterGroupInConcurrency
1 group
2 group
3 group
region_scatterer_test.go:360:
    // For peer, we expect each store have about 50 peers for each group
    checker(scatterer.ordinaryEngine.selectedPeer, 50, 15)
region_scatterer_test.go:353:
    c.Assert(math.Abs(float64(max)-float64(expected)), LessEqual, delta)
... compare_one float64 = 16
... compare_two float64 = 15

CI link

https://ci2.pingcap.net/blue/organizations/jenkins/pd_test/detail/pd_test/4811/pipeline/

Reason for failure (if possible)

expected should be 60.

Anything else