[Gardening][iOS] imported/w3c/web-platform-tests/css/css-anchor-position/popover-implicit-anchor.html is a constant failure

https://bugs.webkit.org/show_bug.cgi?id=301670
rdar://163678748

Unreviewed test gardening

Update test expectation

* LayoutTests/platform/ios/TestExpectations:

Canonical link: https://commits.webkit.org/302323@main

Author: martadarbinyan

LayoutTests/platform/ios/TestExpectations

@@ -8359,3 +8359,5 @@ imported/w3c/web-platform-tests/editing/other/empty-elements-insertion.html [ Fa
 imported/w3c/web-platform-tests/inert/inert-pseudo-element-hittest.html [ Failure ]
 
 webkit.org/b/301655 fast/images/page-wide-animation-toggle.html [ Pass Timeout ]
+
+webkit.org/b/301670 imported/w3c/web-platform-tests/css/css-anchor-position/popover-implicit-anchor.html [ Failure ]