Fix missing [un]collectable_count increments in gctest

Fix missing [un]collectable_count increments in gctest

* tests/test.c [!DBG_HDRS_ALL] (run_one_test): Increment
uncollectable_count instead of collectable_count (for
GC_malloc_uncollectable(0)).
* tests/test.c [!DBG_HDRS_ALL] (run_one_test): Add missing increments
of collectable_count for GC_malloc(8) and GC_malloc(17).
* tests/test.c (run_one_test): Add missing increment of
collectable_count for (void)GC_MALLOC(0).