ProcessExecutor: do not modify mutable objects from parent in forked process #19714

Job	Run time
build_make (ubuntu:24.04)	3m 9s
build_cmake (ubuntu:24.04, true, true)	2m 59s
build_make (ubuntu:25.10)	4m 29s
build_cmake (alpine:3.23, false, false)	4m 16s
build_cmake (ubuntu:25.10, true, true)	3m 4s
build_make (alpine:3.23)	5m 56s
	23m 53s

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