Bug 1591611 - add permissive fuzzy-if for number-selected.html for ubuntu1804 r=jmaher

Changes:

Insert a permissive `fuzzy-if` for the `number-selected.html` test to accommodate ubuntu1804 where the test fails due to large pixel difference.

Once the migration to ubuntu1804 is complete, the permissive range will be tightened such that future deviations can be caught.

Differential Revision: https://phabricator.services.mozilla.com/D57227

--HG--
extra : moz-landing-system : lando

layout/reftests/forms/input/number/reftest.list

@@ -37,7 +37,7 @@ skip-if(Android) == number-max-height-2.html number-max-height-2-ref.html
 fuzzy-if(skiaContent,0-2,0-5) needs-focus == focus-handling.html focus-handling-ref.html
 
 # select
-fuzzy-if(skiaContent,0-1,0-1) == number-selected.html number-selected-ref.html
+fuzzy-if(skiaContent,0-1,0-1) fuzzy-if(gtkWidget,0-181,0-722) == number-selected.html number-selected-ref.html
 
 # pseudo-elements not usable from content:
 == number-pseudo-elements.html number-pseudo-elements-ref.html