statistics: fix the memory leak of region statistics

[rleungx]

What problem does this PR solve?

Issue Number: Close #8710.

What is changed and how does it work?

Check List

Tests

• Unit test

Release note

None.

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lhy1024, okJiang

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[LGTM Timeline notifier]

Timeline:

• 2024-10-15 09:58:20.35822627 +0000 UTC m=+351497.507136216: ☑️ agreed by lhy1024.