Flaky `TestRing_ShuffleShardWithLookback_CorrectnessWithFuzzy`

[dimitarvdimitrov]

The test failed in this run, but succeeded in the retry. Revision was https://github.com/grafana/dskit/pull/214/commits/f73a2dbcda33f09b8e800dcc411b4650da30ce0d

--- FAIL: TestRing_ShuffleShardWithLookback_CorrectnessWithFuzzy (88.81s)
    --- FAIL: TestRing_ShuffleShardWithLookback_CorrectnessWithFuzzy/num_instances_=_9,_num_zones_=_3,_update_oldest_registered_timestamp_=_true (0.02s)
        ring_test.go:1840: random generator seed: 1663955757664614088
        ring_test.go:1958: subring generated after event 4 is expected to include instance instance-6 from ring state at time 2022-09-23 19:11:57.669186493 +0000 UTC m=+4673.344713179 but it's missing (actual instances are: instance-9, instance-10, instance-2)

[bboreham]

Similar:

--- FAIL: TestRing_ShuffleShardWithLookback_CorrectnessWithFuzzy (0.00s)
    --- FAIL: TestRing_ShuffleShardWithLookback_CorrectnessWithFuzzy/num_instances_=_9,_num_zones_=_3,_update_oldest_registered_timestamp_=_false (3.23s)
        ring_test.go:1849: random generator seed: 1697620659695190631
        ring_test.go:1967: subring generated after event 70 is expected to include instance instance-62 from ring state at time 2023-10-18 16:03:39.774918312 +0000 UTC m=+24403.930550466 but it's missing (actual instances are: instance-63, instance-42, instance-61, instance-38, instance-8, instance-53, instance-5, instance-6, instance-45, instance-31, instance-13, instance-17, instance-32, instance-46, instance-19, instance-16, instance-56, instance-21, instance-54, instance-33, instance-4, instance-26, instance-47, instance-12, instance-36, instance-24, instance-40, instance-50, instance-37, instance-49, instance-58, instance-23, instance-30, instance-18, instance-55, instance-28, instance-59, instance-35)

Fail: https://drone.grafana.net/grafana/dskit/3271/1/4 Succeed: https://drone.grafana.net/grafana/dskit/3273/1/4