Fix #14939: Failures to add suppressions are ignored in `importCppcheckGuiProject` #20500

Job	Run time
build_make (ubuntu:24.04)	3m 8s
build_cmake (ubuntu:24.04, true, true)	3m 35s
build_cmake (ubuntu:25.10, true, true)	3m 51s
build_make (ubuntu:25.10)	3m 34s
build_cmake (alpine:3.23, false, false)	4m 40s
build_make (alpine:3.23)	6m 13s
	25m 1s

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