Investigate flaky MempoolTxRebroadcasting system test

System tests are [still flaky in main](https://github.com/cosmos/evm/actions/runs/19079467679/attempts/1) (compare attempt #1 vs attempt #2). Is this a known/tracked flake?

```
=== NAME TestMempoolTxRebroadcasting
require.go:313:
Error Trace: /home/runner/work/evm/evm/tests/systemtests/mempool/test_exceptions.go:59
/home/runner/work/evm/evm/tests/systemtests/mempool/test_exceptions.go:88
Error: Received unexpected error:
failed to send eth legacy tx: failed to broadcast transaction: replacement transaction underpriced: internal [cosmossdk.io/errors@v1.0.2/errors.go:77]
Test: TestMempoolTxRebroadcasting
Messages: failed to send tx
=== NAME TestMempoolTxRebroadcasting/ordering_of_pending_txs_EVM_LegacyTx
testing.go:1811: test executed panic(nil) or runtime.Goexit: subtest may have called FailNow on a parent test
```