Impossible to pass multiple ZIM languages as CSV

[benoit74]

Probably following the upgrade to zimscraperlib 5, it is not possible anymore to pass multiple languages as CSV:

Traceback (most recent call last):
  File "/usr/bin/zimit", line 8, in <module>
    sys.exit(zimit.zimit())
             ~~~~~~~~~~~^^
  File "/app/zimit/lib/python3.13/site-packages/zimit/zimit.py", line 1247, in zimit
    sys.exit(run(sys.argv[1:]))
             ~~~^^^^^^^^^^^^^^
  File "/app/zimit/lib/python3.13/site-packages/zimit/zimit.py", line 852, in run
    res = warc2zim(warc2zim_args)
  File "/app/zimit/lib/python3.13/site-packages/warc2zim/main.py", line 168, in main
    return converter.run()
           ~~~~~~~~~~~~~^^
  File "/app/zimit/lib/python3.13/site-packages/warc2zim/converter.py", line 278, in run
    metadata.LanguageMetadata(self.language)
    ~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^
  File "<@beartype(zimscraperlib.zim.metadata.TextListBasedMetadata.__init__) at 0x7ff107e04900>", line 59, in __init__
  File "/app/zimit/lib/python3.13/site-packages/zimscraperlib/zim/metadata.py", line 297, in __init__
    super().__init__(value=value, name=name)
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^
  File "<@beartype(zimscraperlib.zim.metadata.MetadataBase.__init__) at 0x7ff107da6340>", line 57, in __init__
  File "/app/zimit/lib/python3.13/site-packages/zimscraperlib/zim/metadata.py", line 93, in __init__
    self.value = self.get_cleaned_value(value)
                 ~~~~~~~~~~~~~~~~~~~~~~^^^^^^^
  File "<@beartype(zimscraperlib.zim.metadata.TextListBasedMetadata.get_cleaned_value) at 0x7ff107e04a40>", line 40, in get_cleaned_value
  File "/app/zimit/lib/python3.13/site-packages/zimscraperlib/zim/metadata.py", line 316, in get_cleaned_value
    raise ValueError(
        f"Following code(s) are not ISO-639-3: {','.join(invalid_codes)}"
    )
ValueError: Following code(s) are not ISO-639-3: eng,nld,spa

Probably the problem is that we should not join back with commas the array:

warc2zim/src/warc2zim/language.py

Line 36 in 270f5db

return ",".join(langs)

This should probably be covered by some kind of unit / e2e test, either here or in zimit.