Fix autocomplete for new work item form

What does this MR do and why?

Work Item - support quick actions from `workIte... (#391664 - closed)

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Before	After

How to set up and validate locally

1. In rails console:

   Feature.enable(:work_items_beta)
   Feature.enable(:namespace_level_work_items)

2. Go to epics list page
3. Create new Epic
4. Type / in description