Fix yaml empty node validation #7807

Job	Run time
test	28m 15s
build	5m 52s
lint	8m 2s
integration-configs-db	2m 52s
integration (requires_docker)	6m 4s
integration (integration_alertmanager)	5m 0s
integration (integration_backward_compatibility)	11m 4s
integration (integration_memberlist)	9m 7s
integration (integration_querier)	15m 22s
integration (integration_ruler)	4m 45s
integration (integration_query_fuzz)	3m 19s
deploy	0s
deploy_website	0s
	1h 39m 42s

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