flaky test `TestTuner` in `util/gctuner` pkg

## Bug Report

Flaky runs happened 17 times between "2023-09-01" AND "2023-09-09"

- [CI build](https://do.pingcap.net/jenkins/job/pingcap/job/tidb/job/ghpr_unit_test/32505/)
- [CI build](https://do.pingcap.net/jenkins/job/pingcap/job/tidb/job/ghpr_unit_test/32461/)
- [CI build](https://do.pingcap.net/jenkins/job/pingcap/job/tidb/job/ghpr_unit_test/32451/)
- [CI build](https://do.pingcap.net/jenkins/job/pingcap/job/tidb/job/ghpr_unit_test/32435/)
- [CI build](https://do.pingcap.net/jenkins/job/pingcap/job/tidb/job/ghpr_unit_test/32377/)
- [CI build](https://do.pingcap.net/jenkins/job/pingcap/job/tidb/job/ghpr_unit_test/32370/)
- [CI build](https://do.pingcap.net/jenkins/job/pingcap/job/tidb/job/ghpr_unit_test/32360/)
- [CI build](https://do.pingcap.net/jenkins/job/pingcap/job/tidb/job/ghpr_unit_test/32224/)
- [CI build](https://do.pingcap.net/jenkins/job/pingcap/job/tidb/job/ghpr_unit_test/32213/)
- [CI build](https://do.pingcap.net/jenkins/job/pingcap/job/tidb/job/ghpr_unit_test/32136/)
- [CI build](https://do.pingcap.net/jenkins/job/pingcap/job/tidb/job/ghpr_unit_test/32122/)
- [CI build](https://do.pingcap.net/jenkins/job/pingcap/job/tidb/job/ghpr_unit_test/32026/)
- [CI build](https://do.pingcap.net/jenkins/job/pingcap/job/tidb/job/ghpr_unit_test/31992/)
- [CI build](https://do.pingcap.net/jenkins/job/pingcap/job/tidb/job/ghpr_unit_test/31897/)
- [CI build](https://do.pingcap.net/jenkins/job/pingcap/job/tidb/job/ghpr_unit_test/31821/)
- [CI build](https://do.pingcap.net/jenkins/job/pingcap/job/tidb/job/ghpr_unit_test/31756/)
- [CI build](https://do.pingcap.net/jenkins/job/pingcap/job/tidb/job/ghpr_unit_test/31704/)

Automated flaky test report update.

Repo: pingcap/tidb
Branch: master
Package: pkg/util/gctuner
Case: TestTuner
Flaky Count: 1
Time Thresholded Count: 0
Latest Build: https://do.pingcap.net/jenkins/job/pingcap/job/tidb/job/ghpr_unit_test/339/
Window: 2026-09-14T00:00:00.000Z → 2026-09-15T00:00:00.000Z
Threshold: 100000 ms