tests: fix dfflibmap test - false negative conflict multiple -liberty… #1470

Job	Run time
pre_docs_job	7s
pre_job	36s
Try build docs (html)	1m 11s
Reusable build (ubuntu-latest)	16m 11s
Try build docs (latexpdf)	1m 33s
Reusable build (macos-latest)	10m 6s
Run tests (ubuntu-latest)	12m 37s
Run tests (macos-latest)	13m 54s
Run docs tests (ubuntu-latest)	1m 0s
	57m 15s

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