MAINT Updating _arff.py to v2.4.0 (scikit-learn#13109)

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#### Reference Issues/PRs
Fixes scikit-learn#13103 
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#### What does this implement/fix? Explain your changes.
This PR updates the variable named _RE_ESCAPE_CHARS in _arff.py file line number 168. This updation happens in order to match it with this file(https://github.com/renatopp/liac-arff/blob/master/arff.py) in liac-arff. 


#### Any other comments?


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