fix: correct flutterwave display

[laurelfulford]

All Submissions:

• Have you followed the Newspack Contributing guideline?
• Does your code follow the WordPress' coding standards and VIP Go coding standards?
• 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 some display issues with the Flutterwave Payment Gateway.

Note: this experience is still a bit subpar -- Flutterwave opens in its own iframe inside of the modal checkout, and I haven't gotten it to trigger the thank you step at the very end.

See 1207817176293825-as-1208919243890764

How to test the changes in this Pull Request:

1. Apply this PR and run npm run build.
2. Install the Flutterwave payment gateway: https://wordpress.org/plugins/woo-rave/
3. Under WooCommerce > Settings > Payments, enable the payment gateway and set it to test mode. You can use the keys in the above Asana task:

4. Run through a transaction; on the second screen, confirm you get Flutterwave as a payment gateway:

5. Complete the transaction using Flutterwave; you may get a brief flash of the Order Details, then an iFrame should open:

6. Run a transaction using the test credit card number, 4111 1111 1111 1111. You'll need to fill out additional fake information (billing details).
7. You should get a step to go to your bank to complete the transaction that opens in a new tab:

8. Click the 'Submit' button on the test screen from Flutterwave:

9. Flutterwave should redirect you back to the original tab and show a success message:

10. The success message will then close to the Order Details:

Other information:

• 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]

Setting as a draft to do a bit more digging into whether I can improve the last step.