flaky test TestCTEIterationMemTracker

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)

### 2. What did you expect to see? (Required)

### 3. What did you see instead (Required)

```
testkit.go:274:
Error Trace: pkg/testkit/testkit.go:274
pkg/testkit/testkit.go:199
pkg/testkit/testkit.go:174
pkg/executor/cte_test.go:227
Error: Received unexpected error:
assert row container spill disk failed
github.com/pingcap/tidb/pkg/util.GetRecoverError
pkg/util/util.go:305
github.com/pingcap/tidb/pkg/executor.(*cteProducer).computeRecursivePart.func1
pkg/executor/cte.go:416
runtime.gopanic
GOROOT/src/runtime/panic.go:914
github.com/pingcap/tidb/pkg/executor.(*cteProducer).computeRecursivePart
pkg/executor/cte.go:450
github.com/pingcap/tidb/pkg/executor.(*cteProducer).produce
pkg/executor/cte.go:366
github.com/pingcap/tidb/pkg/executor.(*CTEExec).Next
pkg/executor/cte.go:113
github.com/pingcap/tidb/pkg/executor/internal/exec.Next
pkg/executor/internal/exec/executor.go:410
github.com/pingcap/tidb/pkg/executor.(*ExplainExec).executeAnalyzeExec
pkg/executor/explain.go:130
github.com/pingcap/tidb/pkg/executor.(*ExplainExec).generateExplainInfo
pkg/executor/explain.go:149
github.com/pingcap/tidb/pkg/executor.(*ExplainExec).Next
pkg/executor/explain.go:76
github.com/pingcap/tidb/pkg/executor/internal/exec.Next
pkg/executor/internal/exec/executor.go:410
github.com/pingcap/tidb/pkg/executor.(*ExecStmt).next
pkg/executor/adapter.go:1250
github.com/pingcap/tidb/pkg/executor.(*recordSet).Next
pkg/executor/adapter.go:175
github.com/pingcap/tidb/pkg/session.GetRows4Test
pkg/session/tidb.go:346
github.com/pingcap/tidb/pkg/session.ResultSetToStringSlice
pkg/session/tidb.go:364
github.com/pingcap/tidb/pkg/testkit.(*TestKit).ResultSetToResultWithCtx
pkg/testkit/testkit.go:273
github.com/pingcap/tidb/pkg/testkit.(*TestKit).MustQueryWithContext
pkg/testkit/testkit.go:199
github.com/pingcap/tidb/pkg/testkit.(*TestKit).MustQuery
pkg/testkit/testkit.go:174
github.com/pingcap/tidb/pkg/executor_test.TestCTEIterationMemTracker
pkg/executor/cte_test.go:227
testing.tRunner
GOROOT/src/testing/testing.go:1595
runtime.goexit
src/runtime/asm_amd64.s:1650
Test: TestCTEIterationMemTracker
Messages: sql:explain analyze with recursive cte1 as (select c1 from t1 union all select c1 + 1 c1 from cte1 where c1 < 5000) select * from cte1, args:[]
```
### 4. What is your TiDB version? (Required)

Automated flaky test report update.

Repo: pingcap/tidb
Branch: master
Package: pkg/executor/test/cte
Case: TestCTEIterationMemTracker
Flaky Count: 1
Time Thresholded Count: 0
Latest Build: https://prow.tidb.net/jenkins/job/pingcap/job/tidb/job/pull_unit_test_next_gen/7932/
Window: 2026-08-20T00:00:00.000Z → 2026-08-21T00:00:00.000Z
Threshold: 100000 ms