Mark the window-show-contents-on-map.ui reftest as xfail

We know now what the test is trying to test, just lack
the right plumbing to do it properly. So, keep the test
around, marked as expected fail.

testsuite/reftests/meson.build

@@ -448,6 +448,8 @@ xfails = [
   'sizegroups-evolution-identity-page.ui',
   # these depend on details of text layout
   'label-sizing.ui',
+  # needs a better way to perform delayed actions
+  'window-show-contents-on-map.ui',
 ]
 
 reftest_env = environment()