Fix #14939: Failures to add suppressions are ignored in `importCppcheckGuiProject` #20497

Job	Run time
build_cmake (ubuntu:25.10, true, true)	3m 22s
build_make (ubuntu:25.10)	3m 57s
build_make (ubuntu:24.04)	3m 12s
build_cmake (alpine:3.23, false, false)	4m 45s
build_make (alpine:3.23)	6m 22s
build_cmake (ubuntu:24.04, true, true)	3m 26s
	25m 4s

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