Flaky Test: TestBlocksCleaner_ShouldRemoveBlocksOutsideRetentionPeriod

[SungJin1212]

Describe the bug
The test TestBlocksCleaner_ShouldRemoveBlocksOutsideRetentionPeriod is flaky.
It feels like it's happening quite often..
logs:

--- FAIL: TestBlocksCleaner_ShouldRemoveBlocksOutsideRetentionPeriod (0.19s)
    blocks_cleaner_test.go:770: 
        	Error Trace:	/__w/cortex/cortex/pkg/compactor/blocks_cleaner_test.go:770
        	Error:      	Received unexpected error:
        	            	failed to delete blocks for user: user-2: list block deletion marks: readdirent /tmp/bucket1878592483/user-2/markers: no such file or directory
        	Test:       	TestBlocksCleaner_ShouldRemoveBlocksOutsideRetentionPeriod
FAIL

https://github.com/cortexproject/cortex/actions/runs/16267245987/job/45925644234?pr=6330