[12.0][FIX]l10n_it_sdi_channel: restore python 3.5 compatibility

[aleuffre]

The trailing comma in the arguments of methods such as this one

def _prepare_attachment_in_values(
       self,
       file_name,
       file_content,
       **default_values,
   ):

breaks compatibility with python 3.5. Support for this syntax was added in Python 3.6. It's sufficient to remove the trailing comma after default_values in the 3 methods affected.

[OCA-git-bot]

Hi @sergiocorato,
some modules you are maintaining are being modified, check this out!

[SirTakobi]

Thanks, the CI should have caught that, I have proposed the Python version change in OCA/oca-ci#39, let's see how it goes

[github-actions]

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