Fix Sanitizer API IDL harness test.

The 'sanitizer-api.idl' file was removed in commit bdb3065, because
the API has been integrated into the main DOM / HTML apis. We follow
this by testing the `Sanitizer` object as part of the 'html' idlharness
test.

Ref: bdb3065

The current test seems to fail on all browsers:
https://wpt.fyi/results/sanitizer-api/idlharness.https.window.html?label=experimental&label=master&aligned&q=sanitizer-api%2F

Author: otherdaniel

html/dom/idlharness.https.html

@@ -234,7 +234,8 @@ <h1>HTML IDL tests</h1>
         'localStorage',
         'sessionStorage',
       ],
-      StorageEvent: ['new StorageEvent("storage")']
+      StorageEvent: ['new StorageEvent("storage")'],
+      Sanitizer: ['new Sanitizer({})']
     });
     idlArray.prevent_multiple_testing('HTMLElement');
     await waitForLoad;