gitlab#178 - rsvg-test.c: On 32-bit, allow the maximum difference between color channels to be 10

This is kind of a lousy reason, but i386 is getting max differences of
9 in some text-rendering cases, with respect to the reference files
generated on x86_64.

An explanation of different floating-point units and how i386 uses
80-bit extended precision for everything (by default, at least), while
x86_64 uses different precisions depending on the instructions:

https://stackoverflow.com/questions/22710272/difference-in-floating-point-arithmetics-between-x86-and-x64#22711132

This is more or less a hack, but it will do for now.

GNOME/librsvg#178
4 jobs for 32-bit-ci in 4 minutes and 11 seconds (queued for 3 seconds)
latest
Status Job ID Name Coverage
  Test
failed #10669
fedora:test

00:02:56

failed #10670
fedora:test_release

00:04:11

 
  Lint
skipped #10672
allowed to fail manual
clippy
skipped #10671
allowed to fail manual
rustfmt
 
Name Stage Failure
failed
fedora:test_release Test
make: *** [Makefile:1815: check] Error 2
Running after script...
$ mkdir png_artifacts
$ cp /tmp/*.png png_artifacts
Uploading artifacts...
tests/*.log: found 7 matching files
png_artifacts: found 137 matching files
Uploading artifacts to coordinator... ok id=10670 responseStatus=201 Created token=rfnZnPP5
ERROR: Job failed: exit code 1
failed
fedora:test Test
make: *** [Makefile:1815: check] Error 2
Running after script...
$ mkdir png_artifacts
$ cp /tmp/*.png png_artifacts
Uploading artifacts...
tests/*.log: found 7 matching files
png_artifacts: found 137 matching files
Uploading artifacts to coordinator... ok id=10669 responseStatus=201 Created token=h7HScTmd
ERROR: Job failed: exit code 1