tests: fix a memory leak in test-prio-queue.c

Fix a memory leak in t/helper/test-prio-queue.c, the lack of freeing
the memory with clear_prio_queue() has been there ever since this code
was originally added in b4b594a315 (prio-queue: priority queue of
pointers to structs, 2013-06-06).

By fixing this leak we can cleanly run t0009-prio-queue.sh under
SANITIZE=leak, so annotate it as such with
TEST_PASSES_SANITIZE_LEAK=true.

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

t/helper/test-prio-queue.c

@@ -46,5 +46,7 @@ int cmd__prio_queue(int argc, const char **argv)
 		}
 	}
 
+	clear_prio_queue(&pq);
+
 	return 0;
 }

t/t0009-prio-queue.sh

@@ -1,6 +1,8 @@
 #!/bin/sh
 
 test_description='basic tests for priority queue implementation'
+
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
 cat >expect <<'EOF'