Components: Fix typo for notice color in readme.md

[andreawetzel]

Removed extra characters from applying bold in markdown.

What?

Fixes typo on https://developer.wordpress.org/block-editor/reference-guides/components/notice/

Screenshots or screencast

[github-actions]

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Co-authored-by: andreawetzel <[email protected]>
Co-authored-by: shail-mehta <[email protected]>
Co-authored-by: Mamaduka <[email protected]>

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[github-actions]

👋 Thanks for your first Pull Request and for helping build the future of Gutenberg and WordPress, @andreawetzel! In case you missed it, we'd love to have you join us in our Slack community.

If you want to learn more about WordPress development in general, check out the Core Handbook full of helpful information.

[shail-mehta]

@andreawetzel Thanks for the PR !

LGTM 👍

[Mamaduka]

Thanks, @andreawetzel!