[NKI-421] Gather should work on torch FakeTensor

[ppotapov-aws]

Don't know if it is all it takes 🤷

with FakeTensorMode() as fake_mode:
      fake_a = fake_mode.from_tensor(torch.empty(128, 1, 32, 64, 1, dtype=torch.uint8))
      rv = K.specialize(
        (fake_a,), {"opt": None, "fo": 2}, 2, 1, None, flags
      )
      rv = K.trace(f'./{fname}.out.klr', 'cbor', None)
      rv = json.loads(rv)