Fix console warning after popover removal

What does this MR do and why?

This change makes the reference to the target of the popover optional to prevent a console warning during the removal of a popover (e.g. when v-if="false").

Screenshots or screen recordings

Before

After

How to set up and validate locally

Example below:

1. Visit Admin -> Runners e.g. http://gdk.test:3000/admin/runners?status[]=ACTIVE
2. Open the browser console
3. Filter so no runners are found, so the popover if removed from the page
4. Confirm there are no console warnings/errors.

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.