"generate soroban load" test is flaky

[SirTyson]

Currently, "generate soroban load" is randomly failing in CI. The reason has to do with maxSorobanFail. We can't preflight transactions, so there's some set of tx's that will fail due to insufficient resources. We use maxSorobanFail value to allow some failed transactions due to this issue. However, it looks like this value is too low, as this test has been randomly failing in CI on PRs unrelated to soroban load.