Fix `warn` test for coverage #4723

Job	Run time
lint	52m 49s
test (ubuntu-latest, cargo-dylint)	42m 57s
test (ubuntu-latest, examples)	25m 54s
test (ubuntu-latest, other)	22m 51s
test (macos-latest, cargo-dylint)	1h 6m 1s
test (macos-latest, examples)	43m 10s
test (macos-latest, other)	52m 5s
test (windows-latest, cargo-dylint)	2h 8m 40s
test (windows-latest, examples)	47m 35s
test (windows-latest, other)	1h 7m 50s
all-checks	0s
	9h 9m 52s

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