Flaky test cases in sentinel-parameter-flow-control module

Issue Description

Type: bug report

Describe what happened (or what feature you want)

Flaky unstable test in com.alibaba.csp.sentinel.slots.block.flow.param.ParamFlowDefaultCheckerTest

[ERROR] Tests run: 5, Failures: 1, Errors: 0, Skipped: 0, Time elapsed: 4.823 s <<< FAILURE! - in com.alibaba.csp.sentinel.slots.block.flow.param.ParamFlowDefaultCheckerTest
[ERROR] testParamFlowDefaultCheckSingleValueCheckQpsMultipleThreads(com.alibaba.csp.sentinel.slots.block.flow.param.ParamFlowDefaultCheckerTest)  Time elapsed: 4.063 s  <<< FAILURE!
java.lang.AssertionError: expected:<6> but was:<5>
	at com.alibaba.csp.sentinel.slots.block.flow.param.ParamFlowDefaultCheckerTest.testParamFlowDefaultCheckSingleValueCheckQpsMultipleThreads(ParamFlowDefaultCheckerTest.java:323)

[INFO] Running com.alibaba.csp.sentinel.slots.statistic.metric.HotParameterLeapArrayTest
[INFO] Tests run: 4, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.064 s - in com.alibaba.csp.sentinel.slots.statistic.metric.HotParameterLeapArrayTest
[INFO] Running com.alibaba.csp.sentinel.slots.statistic.data.ParamMapBucketTest
[INFO] Tests run: 2, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.001 s - in com.alibaba.csp.sentinel.slots.statistic.data.ParamMapBucketTest
[INFO] 
[INFO] Results:
[INFO] 
[ERROR] Failures: 
[ERROR]   ParamFlowDefaultCheckerTest.testParamFlowDefaultCheckSingleValueCheckQpsMultipleThreads:323 expected:<6> but was:<5>
[INFO] 
[ERROR] Tests run: 32, Failures: 1, Errors: 0, Skipped: 0

Describe what you expected to happen

The test case should not fail.

How to reproduce it (as minimally and precisely as possible)

Tell us your environment

https://app.circleci.com/pipelines/github/alibaba/Sentinel/473/workflows/ce91869c-8bf7-457e-ba0e-7c0f43dc3c1e/jobs/2520

Anything else we need to know?