[Shortcode-based Checkout] Unblock UI and show a generic error when buyer verification fails.

[iamdharmesh]

All Submissions:

• Does your code follow the WooCommerce Sniffs variant of WordPress coding standards?
• Have you written new tests for your changes, as applicable?
• Have you successfully run tests with your changes locally?
• Will this change require new documentation or changes to existing documentation?

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Changes proposed in this Pull Request:

This PR unblocks the UI and shows a generic error on the Checkout page when the buyer cancels the SCA challenge or buyer verification fails.

Note

We had fixed this issue earlier in PR #265, but it was reintroduced when the verifyBuyer function was removed in PR #342 has reintroduced.

Closes https://linear.app/a8c/issue/SQUARE-132/failing-sca-dialogue-causes-javascript-error

Steps to test the changes in this Pull Request:

1. Try to place order with card 5248 4800 0021 0026 on shortcode based checkout.
2. Cancel the verification Challenge once it shows up.
3. Verify that the Checkout page is unblocked and the page shows a generic error.

Changelog entry

Fix - Unblock UI and show a generic error when buyer verification fails.