test: skip the freemem test on IBMi PASE
On IBMi PASE, the amount of memory in use includes storage used for memory and disks so it is possible to exceed the amount of main storage.
So skip this test on IBMi PASE as libuv --> https://github.com/libuv/libuv/pull/2614/files#diff-564d321f5718b4ed067d21caf87d4b59