WIP: Fix the results propagation concurrent test

[GeoffreyHuck]

Issue: https://github.com/France-ioi/AlgoreaBackend/issues/1067

What the test does

• Launch the result propagation concurrently 30 times
• Note: the result propagation takes a lock with SELECT GET_LOCK("listener_propagate", 10 seconds), with a timeout of 10s, to make sure it's never running concurrently.

Problem

The whole test runs in 1s in my local environment, but on CircleCI, it takes longer than the timeout of 10s, so it fails.

Failed
result_store_integration_test.go:99: 
    result_store_integration_test.go:99: 
    result_store_integration_test.go:99: 
    result_store_integration_test.go:99: 
    result_store_integration_test.go:99: 
    result_store_integration_test.go:99: 
    result_store_integration_test.go:99: 
    ... 
    result_store_integration_test.go:99: