Update cortex_ingester_inflight_push_requests metric description (#6438) #10757

Job	Run time
CodeQL	7m 16s
lint	4m 11s
build	4m 0s
test	15m 44s
test-no-race	7m 42s
integration (requires_docker)	7m 22s
integration (integration_alertmanager)	4m 22s
integration-configs-db	2m 49s
integration (integration_backward_compatibility)	10m 53s
integration (integration_memberlist)	7m 14s
integration (integration_querier)	15m 24s
integration (integration_ruler)	5m 39s
integration (integration_query_fuzz)	4m 58s
deploy_website	1m 2s
deploy	6m 1s
	1h 44m 37s

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