Flaky distributor test RelabelDropWillExportMetricOfDroppedSamples

[yeya24]

Describe the bug

GH action run: https://github.com/cortexproject/cortex/actions/runs/6922198043/job/18828645369

--- FAIL: TestDistributor_Push_RelabelDropWillExportMetricOfDroppedSamples (0.02s)
    distributor_test.go:3367: 
        	Error Trace:	/__w/cortex/cortex/pkg/distributor/distributor_test.go:3367
        	Error:      	Received unexpected error:
        	            	
        	            	
        	            	Diff:
        	            	--- metric output does not match expectation; want
        	            	+++ got:
        	            	@@ -2,2 +2,3 @@
        	            	 # TYPE cortex_discarded_samples_total counter
        	            	+cortex_discarded_samples_total{reason="missing_metric_name",user="user"} 1
        	            	 cortex_discarded_samples_total{reason="relabel_configuration",user="userDistributorPushRelabelDropWillExportMetricOfDroppedSamples"} 1
        	Test:       	TestDistributor_Push_RelabelDropWillExportMetricOfDroppedSamples
FAIL