In order to inherit a JS module in Odoo, it has to return the module declared and in this case you can't because the  website_sale.payment is not returning anything, anyhow, you have another option, 

https://github.com/odoo/odoo/blob/13.0/addons/website_sale/static/src/js/website_sale_payment.js

in the line 6  of the file in the link above you can see that there is a new widget in the widget registry called WebsiteSalePayment, since this is what you want to modify you need to access to this widget and the way to do it is:

var publicWidget = require('web.public.widget');

publicWidget.registry.WebsiteSalePayment.include({

start: function () {
/**

your code here

**/

return this._super.apply(this, arguments);
    },

});