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/t0064-oid-array.sh

@@ -1,6 +1,8 @@
 #!/bin/sh
 
 test_description='basic tests for the oid array implementation'
+
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
 echoid () {