Flaky `TestPartitionRingWatcher_ShouldWatchUpdates`

[dimitarvdimitrov]

example

--- FAIL: TestPartitionRingWatcher_ShouldWatchUpdates (0.05s)
    partition_ring_watcher_test.go:140: 
        	Error Trace:	/home/runner/work/dskit/dskit/ring/partition_ring_watcher_test.go:140
        	Error:      	Not equal: 
        	            	expected: 3
        	            	actual  : 2
        	Test:       	TestPartitionRingWatcher_ShouldWatchUpdates
FAIL