Flaky aggregation test

[kolesnikovae]

Periodically, the Test_Aggregation_Error test fails in CI:

=== Failed
=== FAIL: pkg/distributor/aggregator Test_Aggregation_Error/First_aggregation_failed (0.01s)
    aggregator_test.go:156: 
        	Error Trace:	/home/runner/work/pyroscope/pyroscope/pkg/distributor/aggregator/aggregator_test.go:156
        	Error:      	Target error should be in err chain:
        	            	expected: "context canceled"
        	            	in chain: 
        	Test:       	Test_Aggregation_Error/First_aggregation_failed
    aggregator_test.go:160: 
        	Error Trace:	/home/runner/work/pyroscope/pyroscope/pkg/distributor/aggregator/aggregator_test.go:160
        	Error:      	An error is expected but got nil.
        	Test:       	Test_Aggregation_Error/First_aggregation_failed
        	Messages:   	context canceled
    --- FAIL: Test_Aggregation_Error/First_aggregation_failed (0.01s)

Presumably, it should be caused by the configured 10ms period. One way to solve it is to run test multiple times, or increase the 10ms period (for that specific test)