Flaky test TestAlertmanager_StateReplicationWithSharding_InitialSyncFromPeers

[bboreham]

Error cleared on re-run.

--- FAIL: TestAlertmanager_StateReplicationWithSharding_InitialSyncFromPeers (4.30s)
    --- FAIL: TestAlertmanager_StateReplicationWithSharding_InitialSyncFromPeers/RF_=_2 (1.28s)
        multitenant_test.go:1823: 
            	Error Trace:	multitenant_test.go:1823
            	Error:      	Not equal: 
            	            	expected: 1
            	            	actual  : 0
            	Test:       	TestAlertmanager_StateReplicationWithSharding_InitialSyncFromPeers/RF_=_2
FAIL
FAIL	github.com/cortexproject/cortex/pkg/alertmanager	106.796s

Another flaky test in this area: #4229

[stevesg]

Tracked here #4160

[stale]

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