scheduler: fix fairness ut #7814

Job	Run time
golangci-lint	4m 6s
golangci-lint	3m 58s
unit-tests(Check Go modules)	30s
unit-tests(Check Go modules)	29s
unit-tests(Check manifests)	42s
unit-tests(Check manifests)	30s
unit-tests(Check auto-generated codes)	2m 42s
unit-tests(Check auto-generated codes)	2m 40s
unit-tests(Verify gofmt)	31s
unit-tests(Verify gofmt)	25s
unit-tests(Verify govet)	55s
unit-tests(Verify govet)	52s
unit-tests(Run Go build)	1m 10s
unit-tests(Run Go build)	1m 15s
unit-tests(Run Go test)	5m 6s
unit-tests(Run Go test)	4m 58s
build-and-push (koordlet)	3m 48s
build-and-push (koordlet)	10s
build-and-push (koord-manager)	2m 17s
build-and-push (koord-manager)	17s
build-and-push (koord-scheduler)	3m 19s
build-and-push (koord-scheduler)	18s
build-and-push (koord-descheduler)	2m 54s
build-and-push (koord-descheduler)	19s
	44m 11s

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