tests: fix test-oid-array leak, test in SANITIZE=leak

Fix a trivial memory leak present ever since 38d905bf58 (sha1-array:
add test-sha1-array and basic tests, 2014-10-01), now that that's
fixed we can test this under GIT_TEST_PASSING_SANITIZE_LEAK=true.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/helper/test-oid-array.c

@@ -35,5 +35,9 @@ int cmd__oid_array(int argc, const char **argv)
 		else
 			die("unknown command: %s", line.buf);
 	}
+
+	strbuf_release(&line);
+	oid_array_clear(&array);
+
 	return 0;
 }