Change RuntimeError to ImportError (#17380)
The `onnxruntime-validation` for ORTModule checks for `ImportError`:
https://github.com/microsoft/onnxruntime/blob/44101e877125eaa18e191793973a4e1a002c6eca/onnxruntime/python/onnxruntime_validation.py#L73-L75
If any other kind of error is raised, it does not silently fail and will
raise an exception. This causes a problem when ortmodule is explicitly
not made available on win/mac packages since we currently raise a
RuntimeError.
Resolves issue:
https://github.com/microsoft/onnxruntime-training-examples/issues/161
