safety: fix safeify_url() exception on python 3.11

[half-duplex]

Description

Fixes #2644, or at least makes it not an uncaught exception.

Checklist

• I have read CONTRIBUTING.md
• I can and do license this contribution under the EFLv2
• No issues are reported by make qa (runs make lint and make test)
• I have tested the functionality of the things this change touches

[half-duplex]

Also removed the depluralizing on "1 of 1 engines" since both dgw and I think always-plural is a little less weird there, but that's up for debate.

[Exirel]

Good @ removing pluralization of the error message.

[dgw]

Someone reported another breaking form ([https://www.example.com]) on IRC last night, and I just reconfirmed this PR's fixed behavior. It does indeed fix both the original problem reported in #2644 and this new variant. (Maybe it's not technically a "variant", since the Actual Problem™ is "things inside [square brackets] that aren't IPv6 addresses", but I'm still calling it one.)

I am ready to ship this soon, and even cut an 8.0.2 release since we haven't really gotten any other bug reports against 8.0.1, but things are blocked on getting #2647 or another solution approved & merged so the CI tests will still work.