chainHead/tests: Flaky operation limits test for ensure_operation_limits_works

[lexnv]

Detected by CI run: https://github.com/paritytech/polkadot-sdk/actions/runs/11793900693/job/32850542638?pr=5732

--- TRY 1 STDOUT:        sc-rpc-spec-v2 chain_head::tests::ensure_operation_limits_works ---

running 1 test
test chain_head::tests::ensure_operation_limits_works ... FAILED

failures:

failures:
    chain_head::tests::ensure_operation_limits_works

test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 101 filtered out; finished in 1.48s


--- TRY 1 STDERR:        sc-rpc-spec-v2 chain_head::tests::ensure_operation_limits_works ---
thread 'chain_head::tests::ensure_operation_limits_works' panicked at substrate/client/rpc-spec-v2/src/chain_head/tests.rs:2898:41:
Expected started response
stack backtrace:
   0: rust_begin_unwind
   1: core::panicking::panic_fmt
   2: sc_rpc_spec_v2::chain_head::tests::ensure_operation_limits_works::{{closure}}
   3: tokio::runtime::scheduler::current_thread::Context::enter
   4: tokio::runtime::context::scoped::Scoped<T>::set
   5: tokio::runtime::scheduler::current_thread::CoreGuard::block_on
   6: tokio::runtime::context::runtime::enter_runtime
   7: tokio::runtime::runtime::Runtime::block_on
   8: sc_rpc_spec_v2::chain_head::tests::ensure_operation_limits_works
   9: core::ops::function::FnOnce::call_once
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

 ------------
     Summary [ 507.718s] 4506 tests run: 4501 passed (22 slow, 2 flaky), 5 failed, 4757 skipped
   FLAKY 2/6 [ 244.178s] polkadot-node-core-pvf::it process::execute_worker_killed_during_job
   FLAKY 2/6 [   1.826s] sc-rpc-spec-v2 chain_head::tests::ensure_operation_limits_works

cc @paritytech/subxt-team