Fix donut token2json multiline

[qubvel]

What does this PR do?

Close the issue with token2json processing method for Donut

There is a bug in the implementation of the function token2json in the DonutProcessor class. It doesn't work when there are multilines in a value as shown in the example below. It is related the regex code.

Fixes # (issue)
#30272

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[qubvel]

@NielsRogge could you please review, as you added this model

[amyeroberts]

Thanks for fixing so quickly!

Reviewing as I think @NielsRogge is off today