[JAX] Inherit the existing XLA_FLAGS for the unit tests (#491)

Inherit the existing XLA_FLAGS
Signed-off-by: Reese Wang <rewang@nvidia.com>

qa/L0_jax_unittest/test.sh

@@ -13,6 +13,6 @@ pip install -r $TE_PATH/examples/jax/encoder/requirements.txt
 pytest -Wignore -v $TE_PATH/examples/jax/mnist
 
 # Make encoder tests to have run-to-run deterministic to have the stable CI results
-export XLA_FLAGS="--xla_gpu_deterministic_ops"
+export XLA_FLAGS="${XLA_FLAGS} --xla_gpu_deterministic_ops"
 pytest -Wignore -v $TE_PATH/examples/jax/encoder --ignore=$TE_PATH/examples/jax/encoder/test_multiprocessing_encoder.py
 pytest -Wignore -v $TE_PATH/examples/jax/encoder/test_multiprocessing_encoder.py