[FIX] web: form view set max-width of sheet to real XXL container

On large screen, the sheet in form view has too much space around.
This is due as the `max-width` was set to the `width` of the `XL`
container and not the `XXL`.

Note the size in `$container-max-widths` are:
* sm: 540px
* md: 720px
* lg: 960px
* xl: 1140px
* xxl: 1320px

Steps to reproduce:
* Open a form view with a sheet => BUG

X-original-commit: 27450c9c5d76fee9922a4625f5129b91976a6c55
Part-of: odoo/odoo#101835

addons/web/static/src/views/form/form_controller.scss

@@ -1116,7 +1116,7 @@
 
         > .o_form_sheet {
             width: 100%;
-            max-width: map-get($container-max-widths, xl);
+            max-width: map-get($container-max-widths, xxl);
         }
     }
 }