Fix description of fan service set_direction

[springstan]

Breaking change

Proposed change

Fixes small inaccuracy in the description of the fan service set_direction.
Found while working on home-assistant/home-assistant.io#12179

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

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# Example configuration.yaml

Additional information

• This PR fixes or closes issue: fixes #
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Checklist

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