[IMP] sale_{*}: change label when grouping records without SOL in portal

* = project,timesheet

This commit changes the label when grouping tasks and timesheets by sol in the
portal for records without sol from "No Sales Order Item" to "Not Billed",
which conveys more clearly to the user that the records are not billed.

Task-3278895

addons/sale_project/views/sale_project_portal_templates.xml

@@ -9,7 +9,7 @@
             </th>
             <th t-if="groupby == 'sale_line'" t-attf-colspan="{{grouped_tasks_colspan}}">
                 <span t-if="tasks[0].sudo().sale_line_id" class="text-truncate" t-field="tasks[0].sudo().sale_line_id"/>
-                <span t-else="">No Sales Order Item</span>
+                <span t-else="">Not Billed</span>
             </th>
         </xpath>
     </template>

addons/sale_timesheet/views/sale_timesheet_portal_templates.xml

@@ -30,7 +30,7 @@
                         </t>
                     </t>
                     <t t-else="">
-                        No Sales Order Item
+                        Not Billed
                     </t>
                 </th>
                 <th colspan="1" class="text-end text-muted fw-normal">