flaky TestSampleTracker_Concurrency

[NickAnge]

--- FAIL: TestSampleTracker_Concurrency (0.00s)
    sample_tracker_test.go:154: 
        	Error Trace:	/__w/mimir/mimir/pkg/costattribution/sample_tracker_test.go:154
        	Error:      	Received unexpected error:
        	            	 # HELP cortex_discarded_attributed_samples_total The total number of samples that were discarded per attribution.
        	            	 # TYPE cortex_discarded_attributed_samples_total counter
        	            	-cortex_discarded_attributed_samples_total{reason="__overflow__",team="__overflow__",tenant="user1",tracker="cost-attribution"} 87
        	            	+cortex_discarded_attributed_samples_total{reason="__overflow__",team="__overflow__",tenant="user1",tracker="cost-attribution"} 95
        	            	 # HELP cortex_distributor_received_attributed_samples_total The total number of samples that were received per attribution.
        	            	 # TYPE cortex_distributor_received_attributed_samples_total counter
        	            	-cortex_distributor_received_attributed_samples_total{team="__overflow__",tenant="user1",tracker="cost-attribution"} 87
        	            	+cortex_distributor_received_attributed_samples_total{team="__overflow__",tenant="user1",tracker="cost-attribution"} 95
        	            	 
        	Test:       	TestSampleTracker_Concurrency
FAIL
FAIL	github.com/grafana/mimir/pkg/costattribution	0.090s

https://github.com/grafana/mimir/actions/runs/12872353056/job/35887678041

(In Github CI)

[56quarters]

Another instance:

 --- FAIL: TestSampleTracker_Concurrency (0.00s)
    sample_tracker_test.go:154: 
        	Error Trace:	/__w/mimir/mimir/pkg/costattribution/sample_tracker_test.go:154
        	Error:      	Received unexpected error:
        	            	 # HELP cortex_discarded_attributed_samples_total The total number of samples that were discarded per attribution.
        	            	 # TYPE cortex_discarded_attributed_samples_total counter
        	            	-cortex_discarded_attributed_samples_total{reason="__overflow__",team="__overflow__",tenant="user1",tracker="cost-attribution"} 93
        	            	+cortex_discarded_attributed_samples_total{reason="__overflow__",team="__overflow__",tenant="user1",tracker="cost-attribution"} 95
        	            	 # HELP cortex_distributor_received_attributed_samples_total The total number of samples that were received per attribution.
        	            	 # TYPE cortex_distributor_received_attributed_samples_total counter
        	            	-cortex_distributor_received_attributed_samples_total{team="__overflow__",tenant="user1",tracker="cost-attribution"} 93
        	            	+cortex_distributor_received_attributed_samples_total{team="__overflow__",tenant="user1",tracker="cost-attribution"} 95
        	            	 
        	Test:       	TestSampleTracker_Concurrency
FAIL
FAIL	github.com/grafana/mimir/pkg/costattribution	0.080s

https://github.com/grafana/mimir/actions/runs/12917443513/job/36023847743?pr=10502

[56quarters]

@ying-jeanne Can you take a look at this test?

[56quarters]

I've disabled the test as part of this PR for now since it failed CI a few times in a row.