[0.71][DynamicColorMacOS] Downgrade to warning if appearance is nil

[Saadnajmi]

Cherry-pick of #1885 to 0.71-stable

[github-actions]

	Fails
🚫	❔ This pull request needs a description.
🚫	📋 Missing Changelog - Can you add a Changelog? To do so, add a "## Changelog" section to your PR description. A changelog entry has the following format: [CATEGORY] [TYPE] - Message. CATEGORY may be: General macOS iOS Android JavaScript Internal (for changes that do not need to be called out in the release notes) TYPE may be: Added, for new features. Changed, for changes in existing functionality. Deprecated, for soon-to-be removed features. Removed, for now removed features. Fixed, for any bug fixes. Security, in case of vulnerabilities. MESSAGE may answer "what and why" on a feature level. Use this to briefly tell React Native users about notable changes.

	Warnings
⚠️	🔒 package.json - Changes were made to package.json. This will require a manual import by a Facebook employee.
⚠️	📋 Missing Test Plan - Can you add a Test Plan? To do so, add a "## Test Plan" section to your PR description. A Test Plan lets us know how these changes were tested.
⚠️	scripts/publish-npm.js#L56 - scripts/publish-npm.js line 56 – 'otp' is assigned a value but never used. (no-unused-vars)
⚠️	scripts/publish-npm.js#L123 - scripts/publish-npm.js line 123 – 'major' is assigned a value but never used. (no-unused-vars)
⚠️	scripts/publish-npm.js#L123 - scripts/publish-npm.js line 123 – 'minor' is assigned a value but never used. (no-unused-vars)
⚠️	scripts/publish-npm.js#L123 - scripts/publish-npm.js line 123 – 'prerelease' is assigned a value but never used. (no-unused-vars)
⚠️	scripts/publish-npm.js#L171 - scripts/publish-npm.js line 171 – 'isLatest' is assigned a value but never used. (no-unused-vars)

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