404's from server don't cause error exit status

> Okay, may be I miss something.
>
> I run TaskChampion on https://vision.spb.ru/taskchampion/, and it syncs smoothly.
>
> But when I launch `task rc.sync.server.url=https://vision.spb.ru/404/ sync` (try `curl https://vision.spb.ru/404/`), it just says:
>
> ```
> Syncing with sync server at https://vision.spb.ru/404/
> Configuration override rc.sync.server.url=https://vision.spb.ru/404/
> ```
>
> and returns zero in my case.

_Originally posted by @dluciv in [#3571](https://github.com/GothenburgBitFactory/taskwarrior/issues/3571#issuecomment-2855922106)_