Fix task modal in linked items widget

What does this MR do and why?

Work items now pass around IIDs instead of IDs (from !118060 (merged)) so we also need to update the task modal in the linked items widget to use IIDs

Screenshots or screen recordings

before (note the id in the url)	after (note the iid in the url)

How to set up and validate locally

1. Go to an issue
2. Create a task in the task widget
3. Add the task in the linked items widget
4. Click on the task in the linked items widget
5. Confirm the task opens in the modal and works fine

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.