scheduler: fix flaky test TestRegionLabelDenyScheduler (#8340) #572

Job	Run time
chunks (1, Unit Test(1))	5m 0s
chunks (2, Unit Test(2))	3m 38s
chunks (3, Unit Test(3))	4m 54s
chunks (4, Tests(1))	5m 4s
chunks (5, Tests(2))	5m 1s
chunks (6, Tools Test)	6m 46s
chunks (7, Client Integration Test)	4m 56s
chunks (8, TSO Integration Test)	5m 11s
chunks (9, MicroService Integration(!TSO))	3m 57s
chunks (10, MicroService Integration(TSO))	5m 18s
report-coverage	11s
	49m 56s

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