Fix @ modifier for subquery when split (#6450) #10799

Job	Run time
CodeQL	6m 31s
test	15m 50s
lint	4m 18s
test-no-race	33m 14s
build	4m 1s
integration-configs-db	2m 48s
integration (requires_docker)	7m 18s
integration (integration_alertmanager)	4m 14s
integration (integration_backward_compatibility)	10m 18s
integration (integration_memberlist)	7m 22s
integration (integration_querier)	15m 9s
integration (integration_ruler)	5m 51s
integration (integration_query_fuzz)	4m 47s
deploy_website	50s
deploy	5m 32s
	2h 8m 3s

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