small `Check::instances()` usage cleanup #19768

Job	Run time
build_make (alpine:3.23)	5m 57s
build_cmake (alpine:3.23, false, false)	3m 49s
build_cmake (ubuntu:25.10, true, true)	2m 33s
build_cmake (ubuntu:24.04, true, true)	5m 24s
build_make (ubuntu:24.04)	2m 26s
build_make (ubuntu:25.10)	5m 1s
	25m 10s

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