Fix #14939: Failures to add suppressions are ignored in `importCppcheckGuiProject` #20496

Job	Run time
build_cmake (ubuntu:25.10, true, true)	1m 53s
build_cmake (alpine:3.23, false, false)	1m 22s
build_cmake (ubuntu:24.04, true, true)	1m 58s
build_make (alpine:3.23)	1m 4s
build_make (ubuntu:25.10)	2m 40s
build_make (ubuntu:24.04)	46s
	9m 43s

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