Hide ip address label when ip address is missing

What does this MR do and why?

In some cases, runners don't have an ip address set, we shouldn't show a label next to them.

Screenshots or screen recordings

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How to set up and validate locally

Actually I found it hard to reproduce, but there are a few runners like this in our staging environment, old records that didn't report the IP address and then were removed:

Screenshot of https://staging.gitlab.com/admin/runners?runner_type[]=INSTANCE_TYPE

I still think this fix makes sense, and doesn't hurt users with newer runners.

MR acceptance checklist

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