Use ColorMode enum in nanoleaf

[epenet]

Proposed change

Use ColorMode enum, as follow-up to #69223, and required for #69302

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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[probot-home-assistant]

Hey there @milanmeu, mind taking a look at this pull request as it has been labeled with an integration (nanoleaf) you are listed as a code owner for? Thanks!
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