[FIX] web: gray out sample data group lines in list view

Group lines in a list view of sample date should not be clickable.

Before :
Create a new partner and make an invoice for him in 2020. Post it, and open the partner ledger for 2023. The partner appears. If you unfold his line, you'll see the initial balance amount. So far, so good. Now, click on the "journal items" button on the partner line. Since there is no aml in period for him, it shouldn't show any. Indeed, nothing is shown, and the mockup data are displayed ... However, the "group by partner" filter applied on the list view make is so that group lines are displayed for mockup data ... and they are not greyed and not-clickable as they should.

closes odoo#109733

Task: 3126138
Signed-off-by: Olivier Colson (oco) <[email protected]>

addons/web/static/src/views/list/list_renderer.scss

@@ -452,6 +452,7 @@
 
     .o_data_row,
     .o_list_footer,
+    .o_group_header,
     thead .o_list_record_selector {
         @include o-sample-data-disabled;
     }