poetry export should throw an error when used with an unknown group name

[pmav99]

Specifying an unknown group name on poetry export results in no error whatsoever. E.g.

poetry export --without gibberish && echo OK
poetry export --with gibberish && echo OK

IMHV, unknown group names, at least most of the time, imply typos and should result in an error.

related to: https://github.com/python-poetry/poetry/issues/4576