Fix rollup weight computation

What does this MR do and why?

Trigger roll up weight computation for the current work item when adding or removing a child item

References

• !199856 (comment 2660554388)

How to set up and validate locally

1. Enable the use_cached_rolled_up_weights feature flag
2. Create a task and set a weight on it
3. Create an issue
4. In the "Child items" widget of the issue, add the existing task as a child
5. Refresh the page. The child items widget should show the correct rolled up weight

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.