Default hass_config to contain an empty config

[jbouwh]

Proposed change

Fixture hass_config was introduced with #87981.
The default value of the fixture is None. Bet set to None is is not useful.
In cases where an empty config is needed it would be better to have {} as default.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
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• Breaking change (fix/feature causing existing functionality to break)
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• This PR fixes or closes issue: fixes #
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[home-assistant]

Hey there @home-assistant/core, mind taking a look at this pull request as it has been labeled with an integration (homeassistant) you are listed as a code owner for? Thanks!

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[emontnemery]

Thanks, @jbouwh 👍