tests: Increase reftest tolerance on non-x86_64 even more

filter-component-transfer-from-reference-page fails on Debian i386
with a difference of 14 colour levels around the text "LinearFunc",
but the difference is not visually obvious.

Fixes: #366
Signed-off-by: Simon McVittie <smcv@debian.org>
3 jobs for more-i386-tolerance in 7 minutes and 42 seconds (queued for 25 minutes and 9 seconds)
latest
Status Job ID Name Coverage
  Test
passed #131864
fedora test

00:07:22

 
  Lint
manual #131866
allowed to fail manual
clippy
passed #131865
rustfmt

00:00:20