Fix situation where 'model' can be None (string) in Overkiz

[iMicknl]

Proposed change

(part of https://github.com/home-assistant/core/pull/64092/files split over multiple PR's)

During the strict mypy work, we maked sure that model would always be string, however I didn't notice that self.executor.select_state can return None in some situations where we fallback to the widget.
This widget is an Enum, which was also not used correctly.

Same situation for the sw_version.

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[probot-home-assistant]

Hey there @vlebourl, @tetienne, mind taking a look at this pull request as it has been labeled with an integration (overkiz) you are listed as a code owner for? Thanks!
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[thecode]

Looks good