[FIX] point_of_sale: missing classes on save button

During the bootstrap refactoring we forgot to add some classes to the
save button of the POS (`btn btn-light rounded-0 fw-bolder`) which are
used on the other buttons of the POS.

They are now added to the save button.

closes odoo/odoo#130718

Signed-off-by: Joseph Caburnay (jcb) <jcb@odoo.com>

addons/point_of_sale/static/src/app/screens/product_screen/control_buttons/save_button/save_button.xml

@@ -2,7 +2,7 @@
 <templates id="template" xml:space="preserve">
 
     <t t-name="point_of_sale.SaveButton" owl="1">
-        <div class="control-button" t-on-click="onClick">
+        <div class="control-button btn btn-light rounded-0 fw-bolder" t-on-click="onClick">
             <i class="fa fa-upload" role="img" aria-label="Save" title="Save" />
             Save
         </div>