Bug 1540635: Adjust a fuzzy annotation for reftest 1295466-1.xhtml to be specific to Windows 7, rather than to the "!nativeThemePref" configuration. r=emilio

I'm using "/^Windows\x20NT\x206\.1/.test(http.oscpu)" to check for Windows 7,
which I found (with Win7-related code comments) elsewhere in reftest.list
files.

I'm replacing a "fuzzy-if(!nativeThemePref,...)" annotation here, which I think
was simply mis-applied here -- this test doesn't have any form controls or
theme-related stuff, so it doesn't make sense that its rendering would be
theme-dependent.  I suspect this annotation was added by mistake, due to this
test intermittently failing by coincidence on a try run where the
!nativeThemePref configuration was being tested.

Differential Revision: https://phabricator.services.mozilla.com/D103083

layout/reftests/bugs/reftest.list

@@ -1958,7 +1958,7 @@ fuzzy(0-8,0-1900) fails-if(webrender) == 1291528.html 1291528-ref.html
 # should be same.  |fuzzy()| here allows the difference in border, but not
 # background color.
 fuzzy(0-255,0-1000) skip-if(!cocoaWidget) == 1294102-1.html 1294102-1-ref.html
-fuzzy-if(skiaContent,0-15,0-50) fuzzy-if(gtkWidget,0-14,0-215) fuzzy-if(!nativeThemePref,0-14,0-172) == 1295466-1.xhtml 1295466-1-ref.xhtml #bug 1540635
+fuzzy-if(skiaContent,0-15,0-50) fuzzy-if(gtkWidget,0-14,0-215) fuzzy-if(/^Windows\x20NT\x206\.1/.test(http.oscpu),0-14,0-172) == 1295466-1.xhtml 1295466-1-ref.xhtml #bug 1540635
 fuzzy-if(Android,0-27,0-874) fuzzy-if(!Android,0-14,0-43) == 1313772.xhtml 1313772-ref.xhtml # Bug 1128229, Bug 1389319
 fuzzy(0-3,0-320000) == 1315113-1.html 1315113-1-ref.html
 fuzzy(0-3,0-20000) == 1315113-2.html 1315113-2-ref.html