Fix for librsvg 2.40 on core-updates

[Kaelyn]

Hi,

On core-updates, librsvg-2.40 fails to compile due to a single failing test 
(I've confirmed the failure on x86_64 and i686, though the package is only 
used/needed on non-x86_64 systems for gtk+ and others; it also affects wine and 
wine-staging on x86_64 as they are 32-bit packages). I was able to track down 
the test failure to a text rendering difference between Pango 1.48 and 1.50, 
which led to the text being one pixel line higher between the reference and 
output images. On Monday I submitted https://issues.guix.gnu.org/62646 which 
adds a phase to librsvg-2.40 to adjust the output Y coordinate of the SVG 
transformation matrix by one for the failing test so that it passes with Pango 
1.50.

Cheers,
Kaelyn