fix(checkout-button): handle 10+ product variations

[miguelpeixe]

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:

Increase the pagination limit while fetching product variations in the Checkout Button block and the overflow for the variation modal when users are allowed to select a variation before checkout.

How to test the changes in this Pull Request:

1. While on the release branch, create a product with 20 variations
2. Draft a new page and add a "Checkout Button" block
3. Select the new product, uncheck the "Allow the reader to select the variation before checkout." option, and confirm the dropdown below only renders 10 variations
4. Check the option again, save, visit the page, click the button, and confirm the variation list exceeds the container bounds
5. Check out this branch, refresh the page, click the button, and confirm the variation modal renders a scrollbar
6. Edit the page, uncheck the "Allow the reader to select the variation before checkout." option and confirm all variations render in the dropdown

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?

[matticbot]

🎉 This PR is included in version 1.75.1 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀