about:ion should not be labeled as a Tor Browser page

Summary

In #40002 (closed), we removed about:ion. So, if you go there, you get an error, but it is still recognized as a Tor Browser page.

Steps to reproduce:

1. Open about:ion

What is the current bug behavior?

The page is shown as a Tor Browser page in the location bar.

What is the expected behavior?

I would expect not to see the Tor Browser page label in the location bar.

Environment

Debian GNU/Linux Testing, Tor Browser 11.0.4 (installed long time ago from an official archive, and then updated during time).

Relevant logs and/or screenshots