Unit test "StateChanges OK: multiple concurrent subscriptions" randomly hangs

[StateChanges OK: multiple concurrent subscriptions](https://app.circleci.com/pipelines/github/torquem-ch/silkworm/6642/workflows/913e2a4d-bee3-4e76-b925-be3df7774c8b/jobs/28073)

#!/bin/bash -eo pipefail
cmd/test/node_test

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
node_test is a Catch v2.13.9 host application.
Run with -? for options

-------------------------------------------------------------------------------
BackEndKvServer E2E: KV
StateChanges OK: multiple concurrent subscriptions
-------------------------------------------------------------------------------
/home/builder/project/silkworm/node/backend/remote/backend_kv_server_test.cpp:749
...............................................................................

/home/builder/project/silkworm/node/backend/remote/backend_kv_server_test.cpp:749: FAILED:
{Unknown expression after the reported line}
due to a fatal error condition:
SIGTERM - Termination request signal

===============================================================================
test cases: 4 | 3 passed | 1 failed
assertions: 118 | 117 passed | 1 failed

Too long with no output (exceeded 10m0s): context deadline exceeded