fix(ras-acc): add styles for single country displayed

[laurelfulford]

All Submissions:

• [x] Have you followed the Newspack Contributing guideline?
• [x] Does your code follow the WordPress' coding standards and VIP Go coding standards?
• [x] Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

This PR fixes the display of countries in the modal checkout when you have your shop set to either ship or sell to only one country.

See: 1207817176293825-as-1207991235341043

How to test the changes in this Pull Request:

1. On epic/ras-acc, navigate to WP Admin > WooCommerce > Settings, and set "Selling location(s)" and "Shipping location(s)" to a single country.
2. Run through the modal checkout and note the appearance in the Billing and Shipping sections:

3. Apply this PR and run npm run build.
4. Confirm the appearance of the single country in the modal checkout no longer has a required marker, and is unbolded:

5. Switch one or both of the dropdowns to show more than one country in the WooCommerce settings (either by removing the restriction, or by adding at least one more country to each).
6. Confirm that the dropdown is shown, and it looks like the others with the "required" asterisk.

Other information:

• [x] Have you added an explanation of what your changes do and why you'd like us to include them?
• [ ] Have you written new tests for your changes, as applicable?
• [ ] Have you successfully ran tests with your changes locally?

[laurelfulford]

Thanks @chickenn00dle!