Add a WordPress.org Plugin Repo Icon

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See: https://developer.wordpress.org/plugins/wordpress-org/plugin-assets/#plugin-icons

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@snarfed the plugin uses the 10up GitHub Workflows and these default to .wordpress-org:

• https://github.com/10up/action-wordpress-plugin-asset-update?tab=readme-ov-file#optional-environment-variables
• https://github.com/10up/action-wordpress-plugin-deploy?tab=readme-ov-file#optional-environment-variables