testrunner: do not load `std.cfg` in executor tests (#8419) #19305

Job	Run time
build_make (ubuntu:24.04)	4m 7s
build_make (alpine:3.23)	6m 6s
build_cmake (alpine:3.23, false, false)	4m 39s
build_make (ubuntu:25.10)	4m 57s
build_cmake (ubuntu:25.10, true, true)	5m 56s
build_cmake (ubuntu:24.04, true, true)	5m 16s
	31m 1s

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