Use non_existing_record_id in zoekt API specs

What does this MR do and why?

Use non_existing_record_id in zoekt API specs

As described in #407331 (closed) this is a followup from a previous MR. It is a minor refactoring to the specs to use a clearer non_existing_record_id to simulate not finding a record as opposed to the more hacky approach of adding 100 to the max id.

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

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.

Related to #407331 (closed)