release-26.3: sql/backfill: TestVectorIndexWithPrefixBackfill failed

sql/backfill.TestVectorIndexWithPrefixBackfill [failed](https://mesolite.cluster.engflow.com/invocations/default/254ab4f3-b114-41c7-ba75-52d4c50e0254?testReportRun=1&testReportShard=1&testReportAttempt=1#targets-Ly9wa2cvc3FsL2JhY2tmaWxsOmJhY2tmaWxsX3Rlc3Q=) on release-26.3 @ [769f38f9d3492a70416a81f5ed38c5f09f4b4b83](https://github.com/cockroachdb/cockroach/commits/769f38f9d3492a70416a81f5ed38c5f09f4b4b83):

```
=== RUN TestVectorIndexWithPrefixBackfill
test_log_scope.go:172: test logs captured to: outputs.zip/logTestVectorIndexWithPrefixBackfill332030313
test_log_scope.go:82: use -show-logs to present logs inline
test_server_shim.go:168: automatically injected an external process virtual cluster under test; see comment at top of test_server_shim.go for details.
```

Parameters:
- attempt=1
- race=true
- run=1
- shard=1
Help

See also: [How To Investigate a Go Test Failure \(internal\)](https://cockroachlabs.atlassian.net/l/c/HgfXfJgM)

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Jira issue: CRDB-64944