Use new navigation in admin specs

What does this MR do and why?

This changes **/admin/** specs to use the new navigation.

Part of #420121 (closed).

Screenshots or screen recordings

n/a

How to set up and validate locally

1. Does the pipeline pass?

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.