MC-20548: Refactor sales module email templates to use scalar variables.

Fix variable name in template.

Author: admanesachin

app/design/frontend/Magento/luma/Magento_Sales/email/order_new_guest.html

@@ -8,7 +8,7 @@
 <!--@vars {
 "var formattedBillingAddress|raw":"Billing Address",
 "var order_data.email_customer_note":"Email Order Note",
-"var order.billingAddress.name":"Guest Customer Name",
+"var order.billing_address.name":"Guest Customer Name",
 "var created_at_formatted":"Order Created At (datetime)",
 "var order.increment_id":"Order Id",
 "layout handle=\"sales_email_order_items\" order=$order":"Order Items Grid",