[Flake] TestSafeDoesNotAdvanceWhenUnsafeIsSyncing_NoELP2P: send-on-closed-channel panic in KonaNode shutdown

## Test

`TestSafeDoesNotAdvanceWhenUnsafeIsSyncing_NoELP2P` in `op-acceptance-tests/tests/sync/elsync/gap_elp2p`

## Symptom

Same `panic: send on closed channel` in `op-devstack/sysgo/l2_cl_kona.go:72` (KonaNode shutdown) that affects sibling test `TestELP2PFCUUnavailableHash`. Almost certainly the same root cause — both tests in the same package fail together with the same panic when this flake fires.

## Frequency

8 flakes in last 90 days per CircleCI Insights, job `memory-all-kona-op-reth` / `memory-all-opn-op-reth`.

## Latest occurrence

PR #21045, CircleCI job 5119174:
- https://circleci.com/gh/ethereum-optimism/optimism/5119174

## Relationship

This issue is filed separately from the sibling test for tracking purposes, but the fix is expected to be the same change in `op-devstack/sysgo/l2_cl_kona.go`. If the fixer confirms one root cause, this issue may be closed by the same PR.

See companion issue for the sibling test.

(Filed by Claude on behalf of @Maurelian. A `flake-fixer` agent has been launched against this test.)