oversized-region is not zero after the workload has stopped for a long time

## Bug Report

### What did you do?
run：endless-oltp-dynamic-regions-update-config-repeatedly-stability

### What did you expect to see?
oversized-region is zero after the workload has stopped for a long time

### What did you see instead?
oversized-region is not zero after the workload has stopped for a long time
[oversized-region.txt](https://github.com/tikv/pd/files/9207826/oversized-region.txt)

### What version of PD are you using (`pd-server -V`)?
./tikv-server -V
TiKV
Release Version: 6.2.0-alpha
Edition: Community
Git Commit Hash: 7dedb3a462479d4ddcde7361358fefab44f0a844
Git Commit Branch: heads/refs/tags/v6.2.0
UTC Build Time: 2022-07-26 10:09:31
Rust Version: rustc 1.62.0-nightly (7c4b47696 2022-04-30)
Enable Features: pprof-fp jemalloc mem-profiling portable sse test-engine-kv-rocksdb test-engine-raft-raft-engine cloud-aws cloud-gcp cloud-azure
Profile: dist_release
./pd-server -V
Release Version: v6.2.0
Edition: Community
Git Commit Hash: c643f3f96f2ac51c63267e6d120adecb2ba978e5
Git Branch: heads/refs/tags/v6.2.0
UTC Build Time: 2022-07-26 10:04:28
./tidb-server -V
Release Version: v6.2.0
Edition: Community