Bug 1716866 - set html/semantics/embedded-content/the-iframe-element/iframe_sandbox_block_modals-4.html as passing

Test started to pass after bug 1716866 had landed.

Differential Revision: https://phabricator.services.mozilla.com/D131810

testing/web-platform/meta/html/semantics/embedded-content/the-iframe-element/iframe_sandbox_block_modals-4.html.ini

@@ -1,5 +0,0 @@
-[iframe_sandbox_block_modals-4.html]
-  expected: TIMEOUT
-  [Frames without `allow-modals` should not be able to open modal dialogs]
-    expected: TIMEOUT
-