Flaky test: TestRing_ShuffleShard_Consistency

[dsabsay]

--- FAIL: TestRing_ShuffleShard_Consistency (8.23s)
    --- FAIL: TestRing_ShuffleShard_Consistency/instances_=_20,_shard_size_=_12,_ring_operation_=_add-instance (0.27s)
        ring_test.go:1981: 
            	Error Trace:	/__w/cortex/cortex/pkg/ring/ring_test.go:1981
            	Error:      	"2" is not less than or equal to "1"
            	Test:       	TestRing_ShuffleShard_Consistency/instances_=_20,_shard_size_=_12,_ring_operation_=_add-instance
        ring_test.go:1982: 
            	Error Trace:	/__w/cortex/cortex/pkg/ring/ring_test.go:1982
            	Error:      	"2" is not less than or equal to "1"
            	Test:       	TestRing_ShuffleShard_Consistency/instances_=_20,_shard_size_=_12,_ring_operation_=_add-instance

Seen on #6584