Fix exit code test for unix platform #282

Job	Run time
tests (3.2, 7.2)	10m 7s
tests (3.1, 7.2)	10m 35s
tests (3.2, edge)	8s
tests (3.1, 7.1)	9m 24s
tests (3.2, 8.0)	10m 10s
tests (3.4, 7.2)	5m 44s
tests (3.3, 8.0)	5m 48s
tests (3.4, 8.0)	5m 45s
tests (3.4, 7.1)	5m 22s
tests (head, edge)	32s
tests (head, 8.0)	27s
tests (3.3, 7.2)	5m 37s
tests (3.2, 7.1)	10m 28s
tests (3.3, 7.1)	5m 27s
tests (3.4, edge)	39s
tests (head, 7.1)	23s
tests (head, 7.2)	23s
tests (3.3, edge)	39s
tests (3.3, 7.1, --enable-frozen-string-literal)	5m 30s
	1h 33m 8s

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