### Steps to reproduce

- Install `sale_timesheet_enterprise`.
- Go to **Tasks → All Tasks**.
- Switch to the **Gantt** view.
- Group by **Sale Order Item** (`sale_line_id`).

### Issue

A traceback is raised when loading the Gantt view with group by `sale_line_id`:

```text
ValueError: Invalid field 'planned_hours' on model 'project.task' for 'planned_hours:sum'
```

### Root cause

The Gantt progress bar computation for the `sale_line_id` grouping performs a `_read_group()` aggregation on the `planned_hours` field of `project.task`.

However, `planned_hours` was renamed to `allocated_hours` during the saas-16.5 migration, so the former field no longer exists on `project.task`. As a result, the aggregation raises a `ValueError`.

Migration reference:
https://github.com/odoo/upgrade/blob/e638c6ce00d9d8936d034ad7130fef51565b9195/migrations/project/saas~16.5.1.2/pre-migrate.py#L10

Issued PR: https://github.com/odoo/enterprise/pull/49685

### Fix

Use `allocated_hours`, the renamed equivalent of `planned_hours`, when computing the Gantt progress bar. This restores the Gantt view when grouping tasks by **Sale Order Item** and prevents the traceback.

Forward-Port-Of: odoo/enterprise#122297