bug#57691: 29.0.50; image-tests failures

[Eli Zaretskii]

> From: Stefan Kangas <stefankangas@gmail.com>
> Date: Fri, 9 Sep 2022 08:44:19 -0400
> Cc: 57691@debbugs.gnu.org
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> This looks like some version of librsvg giving a different error
> >> message.  Does the attached patch fix this for you?
> >
> > Yes, thanks.
> >
> >> Also, out of interest, do you know which version of librsvg you're
> >> using?
> >
> > 2.40.1.
> 
> Mine is 2.50.3

librsvg 2.40.x is the last version that doesn't need a Rust compiler
to build, so I think we should keep it supported for the observable
future.