[Bug] onnxscript installed by 'pip install -e .' does not work outside of project root directory

[BowenBao]

Repro:

pip install -e .

Under project root directory:

python
>>> import onnxscript
>>> dir(onnxscript)
['BFLOAT16', 'BOOL', 'COMPLEX128', 'COMPLEX64', 'DOUBLE', 'FLOAT', 'FLOAT16', 'FLOAT8E4M3FN', 'FLOAT8E4M3FNUZ', 'FLOAT8E5M2', 'FLOAT8E5M2FNUZ', 'INT16', 'INT32', 'INT64', 'INT8', 'OnnxFunction', 'STRING', 'TracedOnnxFunction', 'UINT16', 'UINT32', 'UINT64', 'UINT8', '__all__', '__builtins__', '__cached__', '__doc__', '__file__', '__loader__', '__name__', '__package__', '__path__', '__spec__', '__version__', '_internal', 'backend', 'converter', 'export_onnx_lib', 'external_tensor', 'graph', 'importlib', 'irbuilder', 'main', 'onnx_opset', 'onnx_types', 'opset1', 'opset10', 'opset11', 'opset12', 'opset13', 'opset14', 'opset15', 'opset16', 'opset17', 'opset18', 'opset19', 'opset2', 'opset3', 'opset4', 'opset5', 'opset6', 'opset7', 'opset8', 'opset9', 'opset_ai_onnx_ml1', 'opset_ai_onnx_ml2', 'opset_ai_onnx_ml3', 'proto2python', 'script', 'sourceinfo', 'tensor', 'type_annotation', 'values']
>>>

Now go to any other directory

cd tests
python
>>> import onnxscript
>>> dir(onnxscript)
['__doc__', '__file__', '__loader__', '__name__', '__package__', '__path__', '__spec__']
>>>

Installing onnxscript with python setup.py develop does not exhibit this issue.