Add utf-8 encoding for extractors::python::_open

[arkid15r]

Fixes

File "G:\python-holidays\env\Lib\site-packages\lingva\extractors\python.py", line 125, in __call__
    line = self.readline()
           ^^^^^^^^^^^^^^^
  File "C:\Program Files\Python312\Lib\encodings\cp1252.py", line 23, in decode
    return codecs.charmap_decode(input,self.errors,decoding_table)[0]
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
UnicodeDecodeError: 'charmap' codec can't decode byte 0x81 in position 2670: character maps to <undefined>

[KJhellico]

LGTM!