Revert "test (ex/llm): Removed onnx dependency when collecting tests."

This reverts commit d4509c6.

tests/brevitas_examples/test_llm.py

@@ -8,6 +8,7 @@
 import shutil
 
 import numpy as np
+import onnx
 import pytest
 import torch
 
@@ -331,9 +332,6 @@ def onnx_export_args(default_run_args, request):
 @jit_disabled_for_export()
 @requires_pt_ge('2.2')
 def test_small_models_onnx_export(caplog, onnx_export_args):
-    import onnx
-
-    from brevitas_examples.llm.main import main
     caplog.set_level(logging.INFO)
     args = onnx_export_args
     float_ppl, quant_ppl, model = main(args)