Incorrect conversion from tf dtype to jax dtype

[backpropper]

In class DatasetInputSpecsProvider when converting tf specs to jax

praxis/praxis/base_input.py

Line 1116 in dd07dd6

dtype=spec.dtype.as_numpy_dtype())

as_numpy_dtype is considered as a method when it is actually an attribute of tf.dtypes.Dtype (https://www.tensorflow.org/api_docs/python/tf/dtypes/DType#attributes).

The code works for most dtypes but fails to do for tf.string as the returned entity is a pointer to the object np datatype and not the object datatype itself.