display icon for ppcp-card-button-gateway in the checkout

functions.php

<?php

function woocommerce_paypal_payments_card_button_gateway_icon( $icon, $id ) {
    if ( $id === 'ppcp-card-button-gateway' ) {
        return '<img src="https://upload.wikimedia.org/wikipedia/commons/2/2a/Mastercard-logo.svg" alt="Mastercard" /> <img src="https://upload.wikimedia.org/wikipedia/commons/0/04/Visa.svg" alt="Visa" /> <img src="https://www.paypalobjects.com/webstatic/mktg/Logo/pp-logo-100px.png" alt="PayPal Payments" />'; 
    } else {
        return $icon;
    }
}
add_filter( 'woocommerce_gateway_icon', 'woocommerce_paypal_payments_card_button_gateway_icon', 10, 2 );