Add check for restricted contributors

[ernilambar]

Add check for restricted contributors.

These are few frequent encounters where readme is generated from some third party readme generator and plugin author forget to update the Contributors value in readme:

$restricted_contributors = array(
	'username',
	'your-username',
	'your_wordpress_username',
	'yourusername',
);

Edit: Add sample output

[github-actions]

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Co-authored-by: ernilambar <rabmalin@git.wordpress.org>
Co-authored-by: swissspidy <swissspidy@git.wordpress.org>
Co-authored-by: davidperezgar <davidperez@git.wordpress.org>

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.