[mlir][python] Temporarily disable test for converting unsupported...

[mlir][python] Temporarily disable test for converting unsupported DenseElementsAttr types to a buffer.

* Need to investigate the proper solution to https://github.com/pybind/pybind11/issues/3336 or engineer something different.
* The attempt to produce an empty buffer_info as a workaround triggers asan/ubsan.
* Usage of this API does not arise naturally in practice yet, and it is more important to be asan/crash clean than have a solution right now.
* Switching back to raising an exception, even though that triggers terminate().