s_donation: fix button showing whitespace before modifying list

Author: agau-odoo

addons/website_payment/static/src/snippets/s_donation/000.scss

@@ -2,6 +2,7 @@
     @include o-input-number-no-arrows();
 
     .s_donation_btn {
+        display: inline-flex; // Don't print whitespace between currency and text node
         transition: background 0.2s;
 
         &:focus {