Shopware Payments: PayPal Smart Payment Buttons available despite error in checkout

### Shopware Version

6.7.13.0 with Shopware Payments 3.2635.2

### Affected area / extension

Extension:Shopware-Payments

### Actual behaviour

When an error would normally prevent checkout (such as incomplete address), the Smart Payment Buttons are still available and can be used to pay.

This does not happen in SwagPayPal - there they are disabled until the error is fixed.

### Expected behaviour

The Smart Payments Buttons remain disabled until any error preventing checkout is fixed

### How to reproduce

- Set up a shop with Shopware Payments
- Create a customer account with minimal address and log in
- After creating the account, set address line 2 as mandatory
- Proceed to checkout with a product, the checkout will show an error that the address is incomplete
- When selecting PayPal via Shopware Payments, the Smart Payments Buttons will be available

Start by reproducing the checkout with a mandatory address line 2 and an incomplete address, then inspect the Shopware Payments Smart Payment Buttons integration and compare its behavior with SwagPayPal. Done means the Smart Payment Buttons remain disabled whenever a checkout-blocking error is present and become available after the error is fixed.

Written by the indexing model from the issue text.