Bug 1563717 - Mark pinch-zoom-position-sticky.html as failing on webrender. r=tnikkel

WebRender handling of position:sticky is buggy in the presence of zooming.
The fix for bug 1563717 exposes this bug in pinch-zoom-position-sticky.html.

Differential Revision: https://phabricator.services.mozilla.com/D39574

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

gfx/layers/apz/test/reftest/reftest.list

@@ -30,4 +30,4 @@ skip-if(!asyncPan) == frame-reconstruction-scroll-clamping.html frame-reconstruc
 # Test that position:fixed and position:sticky elements are attached to the
 # layout viewport.
 pref(apz.allow_zooming,true) == pinch-zoom-position-fixed.html pinch-zoom-position-fixed-ref.html
-pref(apz.allow_zooming,true) == pinch-zoom-position-sticky.html pinch-zoom-position-sticky-ref.html
+pref(apz.allow_zooming,true) fails-if(webrender) == pinch-zoom-position-sticky.html pinch-zoom-position-sticky-ref.html  # bug 1569339 for webrender