[FIX] web: grouped list view: group header layout

This rev. ensures that the group name is vertically centered inside
the group header row. Padding rules have been moved from enterprise
to community.

Task 1878254

closes odoo/odoo#27603

addons/web/static/src/scss/list_view.scss

@@ -93,8 +93,10 @@
 
     // Grouped list views
     tbody > tr.o_group_header {
-        height: 31px;
-
+        > th, > td {
+            padding-top: ($table-cell-padding-sm*2);
+            padding-bottom: ($table-cell-padding-sm*2);
+        }
         .o_group_name {
             white-space: nowrap;
         }