fix(retainer): fix qlc cursor cleanup

[savonarola]

Fixes EMQX-12319

Release version: e5.7.0

Summary

PR Checklist

Please convert it to a draft if any of the following conditions are not met. Reviewers may skip over until all the items are checked:

• [x] Added tests for the changes
• [na] Added property-based tests for code which performs user input validation
• [x] Changed lines covered in coverage report
• [ ] Change log has been added to changes/(ce|ee)/(feat|perf|fix|breaking)-<PR-id>.en.md files
• [x] For internal contributor: there is a jira ticket to track this change
• [x] Schema changes are backward compatible