Bug 1495499 [wpt PR 13288] - Update wpt metadata, a=testonly

wpt-pr: 13288
wpt-type: metadata

testing/web-platform/meta/feature-policy/experimental-features/lazyload/lazyload-image-attribute-on-sanity-check-tentative.sub.html.ini

@@ -0,0 +1,4 @@
+[lazyload-image-attribute-on-sanity-check-tentative.sub.html]
+  [Verify 'lazyload' attribute state 'on' works as expected: image loads only when in viewport.]
+    expected: FAIL
+