Flaky TestSchedulerProcessor_processQueriesOnSingleStream

[pracucci]

Seen a flaky run of TestSchedulerProcessor_processQueriesOnSingleStream (CI):

--- FAIL: TestSchedulerProcessor_processQueriesOnSingleStream (1.65s)
    --- FAIL: TestSchedulerProcessor_processQueriesOnSingleStream/should_not_cancel_query_execution_if_scheduler_client_returns_a_non-cancellation_error (0.51s)
        scheduler_processor_test.go:253: 
            	Error Trace:	/__w/mimir/mimir/pkg/querier/worker/scheduler_processor_test.go:253
            	Error:      	Not equal: 
            	            	expected: 2
            	            	actual  : 1
            	Test:       	TestSchedulerProcessor_processQueriesOnSingleStream/should_not_cancel_query_execution_if_scheduler_client_returns_a_non-cancellation_error
            	Messages:   	Expected number of calls (2) does not match the actual number of calls (1).
FAIL
FAIL	github.com/grafana/mimir/pkg/querier/worker	4.198s