Trying to add ancestor epic as child epic results in confusing error message

Summary

When an epic has an ancestor (that the user may not be aware of) and is trying to add the ancestor as a child epic, the error message reads We cannot find an epic that matches you are looking for. It should instead read the epic you are trying to add cannot be added as it is an ancestor (or something).

Basically, like #33093 (closed) but for epics.

Steps to reproduce

• navigate to epic in a subgroupd (for example issue-reproduce/public_issues&1)
• try to add a child epic (for example issue-reproduce/public_issues&2)

What is the current bug behavior?

Child epic cannot be added, because it's an ancestor, but the error message does not make that clear, making the rejection reason a mystery.

(issue-reproduce/public_issues&1)

What is the expected correct behavior?

Child epic cannot be added, and the error message makes it clear why (because the child epic is in fact one of the current epic's ancestors).

(issue-reproduce&5)