### Describe Your Changes
Add test cases proving that it is possible to lose indexDB after
changing the retention period. See #7609
### Checklist
The following checks are **mandatory**:
- [x ] My change adheres [VictoriaMetrics contributing
guidelines](https://docs.victoriametrics.com/contributing/).
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Signed-off-by: Artem Fetishev <rtm@victoriametrics.com>
Co-authored-by: Roman Khavronenko <roman@victoriametrics.com>