[Bug]: TestCheckLeaseFailed intermittently leaves ISCP watermark at 0-0

## Summary

The unsharded Ubuntu/x86 race UT intermittently fails `pkg/vm/engine/test.TestCheckLeaseFailed` because the ISCP watermark remains at `0-0` instead of reaching the expected HNSW job watermark. This is an untouched-subsystem flaky candidate, not a compile, type, static-analysis, security, or stable product-error failure.

## Source PR and failed checks

- PR: https://github.com/matrixorigin/matrixone/pull/28633
- Branch: `m-28618`
- Exact head: `d0d1b70daa982c8a8da53e4199629f91bd7f3edd`
- Run attempt 2: https://github.com/matrixorigin/matrixone/actions/runs/34490540322
- UT job: https://github.com/matrixorigin/matrixone/actions/runs/34490540322/job/103098611703
- Required-check job: https://github.com/matrixorigin/matrixone/actions/runs/34490540322/job/103111716025
- CI command: `make ut UT_CONFIGURED=1 UT_PARALLEL=6 UT_TIMEOUT=40 UT_SHARD=all`

## Failure signature

The complete failed-job log records:

```text
TestCheckLeaseFailed
change_handle_test.go:3210: Condition never satisfied
change_handle_test.go:3232: ISCP watermark did not reach expected state
account=0 table=16390 job=hnsw_idx expectation=reach 1789089214068965429-0 observed=true found=true current=0-0
--- FAIL: TestCheckLeaseFailed (22.21s)
```

The surrounding `rpc client closed` messages occur during teardown; the stable test failure is the unmet ISCP watermark assertion above.

## Independence evidence

Using the repository's `mo-cgo-test` wrapper with the CI race/tags/mode, the exact focused command was:

```text
.agents/skills/mo-dev/scripts/mo-cgo-test -race -tags matrixone_test -vet=off -short -count=1 -timeout=40m -p 1 -run '^TestCheckLeaseFailed$' ./pkg/vm/engine/test
```

- The exact PR head passed 3/3 independent runs.
- Clean detached `up/main` at `e7d46d6dfb27696211ca828c55e245d3bd1b634d` passed the same command 3/3.
- The PR changes only `pkg/frontend/authenticate.go`, `pkg/frontend/load_preplan_auth_test.go`, `pkg/frontend/mysql_cmd_executor.go`, and `pkg/tests/arrowload/arrow_load_lifecycle_test.go`. Neither the changed-file closure nor the test harness touches `pkg/vm/engine/test`, ISCP lease/watermark handling, HNSW propagation, or the embedded-cluster path used by this test.
- The other CI gates and the Arrow LOAD package lane passed; the failed UT job reported this case and an unrelated logservice race only.

## Reproduction

From a clean checkout, run the focused command above three times with the repository's CGo test wrapper. The CI failure was observed in the full unsharded command listed above under Ubuntu/x86 race execution.

The permitted failed-job rerun for run 34490540322 was already accepted and completed as attempt 2. Because this exact run has already consumed its one rerun, no additional rerun is requested here.