Indeterministic test failure in `SpillPool`

### Describe the bug

The failed test: https://github.com/apache/datafusion/blob/af771970b738f56425b50375cc03b6732a864282/datafusion/physical-plan/src/spill/spill_pool.rs#L414

It failed in one CI test run, however it can't be reproduced through repeated runs. It can be a heisenbug.
https://github.com/apache/datafusion/actions/runs/21394691626/job/61590390139?pr=20026

### To Reproduce

_No response_

### Expected behavior

_No response_

### Additional context

_No response_

Start with datafusion/physical-plan/src/spill/spill_pool.rs at the test near line 414, then inspect the linked CI job for the intermittent failure details. The issue provides no reproduction steps or explicit completion criteria, so investigate the cause and establish reliable evidence that the failure no longer occurs.

Written by the indexing model from the issue text.