onnxruntime

Refine `op_types_to_quantize` argument handling in matmul_4bits_quantizer.py (#21815)

### Description
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Refine `op_types_to_quantize` argument handling in
matmul_4bits_quantizer.py

### Motivation and Context
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- If it fixes an open issue, please link to the issue here. -->
The default `op_types_to_quantize "MatMul"` will cause
`tuple(args.op_types_to_quantize)` to become `('M', 'a', 't', 'M', 'u',
'l')`, which is not expected.