Add missing slice sort for user scanner unit test #8178

Job	Run time
lint	16m 27s
build	3m 55s
test	18m 2s
integration-configs-db	1m 55s
integration (requires_docker)	5m 3s
integration (integration_alertmanager)	3m 43s
integration (integration_backward_compatibility)	17m 34s
integration (integration_memberlist)	7m 20s
integration (integration_querier)	12m 29s
integration (integration_ruler)	3m 49s
integration (integration_query_fuzz)	1m 54s
deploy_website	0s
deploy	0s
	1h 32m 11s

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