Bug 1509775 [wpt PR 14229] - Update wpt metadata, a=testonly

wpt-pr: 14229
wpt-type: metadata

testing/web-platform/meta/preload/link-header-preload-srcset.tentative.html.ini

@@ -2,3 +2,6 @@
   [Makes sure that Link headers preload images with (experimental) srcset/imgsizes attributes.]
     expected: FAIL
 
+  [Makes sure that Link headers preload images with (experimental) imagesrcset/imagesizes attributes.]
+    expected: FAIL
+