[Functionalization] Properly skip GRU and LSTM tests (#4789)
Summary:
test_GRU_grad_and_gradgrad_xla_float64 and test_LSTM_grad_and_gradgrad_xla_float64
have been failing for a long time for the same reason in TPU. Not sure if
it worth fixing these two tests just for CPU/GPU. Let's skip them.
Test Plan:
CI.
